Add prose tests

[bkeepers]

This adds script/test-prose, which uses several node packages that check for proper english, readability, insensitive language, and phrases that could be simplified.

It's all very configurable, so as we develop a clearer styleguide, we could add more checks to this. I'm not sure that we'd ever want to enforce these checks, but it's at least helpful to see them.

Note that this PR is based on the content in #8, so it includes that in the diff as well.

Here's the output:

$ script/test-prose 
reporting
_content/getting-started/branding.md
  21:213-21:295  warning  Quite hard to read sentence
  27:1-27:170    warning  Quite hard to read sentence
  29:58-29:60    warning  `he` may be insensitive, use `they`, `it` instead  he-she
  31:455-31:462  warning  Remove “overall”                                   overall
  33:227-33:231  warning  Remove “very”                                      very
  35:1-35:62     warning  Don’t use literal URLs without angle brackets      no-literal-urls
  35:1-35:62     warning  Very hard to read sentence
  39:202-39:212  warning  Replace “anticipate” with “expect”                 anticipate
  45:4-45:67     warning  Very hard to read sentence

_content/getting-started/index.md
  5:75-5:124     warning  Very hard to read sentence
  11:52-11:58    warning  Replace “option” with “choice”                                option
  13:1-13:168    warning  Quite hard to read sentence
  15:32-15:43    warning  Replace “comply with” with “follow”                           comply with
  19:63-19:74    warning  Replace “In terms of” with “as”, “for”, “with”, or remove it  in terms of
  21:1-21:10     warning  Remove “There are”                                            there are
  23:110-23:448  warning  Very hard to read sentence
  25:269-25:413  warning  Quite hard to read sentence
  25:353-25:361  warning  Replace “multiple” with “many”                                multiple
  27:240-27:245  warning  Remove “it is”                                                it is

_content/getting-started/preparing.md
  12:1-12:170    warning  Very hard to read sentence
  16:1-16:127    warning  Quite hard to read sentence
  18:44-18:53    warning  Remove “there are”                                                         there are
  27:60-27:66    warning  Replace “option” with “choice”                                             option
  27:163-27:220  warning  Very hard to read sentence
  29:27-29:36    warning  Replace “selection” with “choice”                                          selection
  46:140-46:144  warning  Remove “very”                                                              very
  50:1-50:130    warning  Quite hard to read sentence
  54:48-54:59    warning  Replace “participate” with “take part”                                     participate
  56:1-56:12     warning  Replace “In addition” with “also”, “besides”, “too”                        in addition
  56:1-56:124    warning  Very hard to read sentence
  58:79-58:86    warning  Replace “solicit” with “ask for”, “request”                                solicit
  58:134-58:341  warning  Very hard to read sentence
  58:329-58:340  warning  Replace “participate” with “take part”                                     participate
  62:156-62:163  warning  Replace “request” with “ask”                                               request
  70:80-70:88    warning  Replace “maintain” with “support”, “keep”                                  maintain
  70:222-70:308  warning  Quite hard to read sentence
  70:256-70:266  warning  Replace “facilitate” with “ease”, “help”                                   facilitate
  70:309-70:442  warning  Quite hard to read sentence
  70:443-70:518  warning  Don’t pad `strong` with inner spaces                                       no-inline-padding
  70:446-70:516  warning  Quite hard to read sentence
  70:508-70:514  warning  `actors` may be insensitive, use `performers`, `stars`, `artists` instead  actors-actresses
  72:1-72:12     warning  Replace “In addition” with “also”, “besides”, “too”                        in addition
  72:1-72:166    warning  Quite hard to read sentence
  78:204-78:212  warning  Replace “multiple” with “many”                                             multiple
  83:3-84:30     warning  Missing blank line before block node                                       no-missing-blank-lines
  83:5-83:65     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  84:5-84:30     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  86:3-90:42     warning  Missing blank line before block node                                       no-missing-blank-lines
  86:5-86:76     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  86:5-86:76     warning  Very hard to read sentence
  87:5-87:52     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  88:5-88:69     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  89:5-89:66     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  90:5-90:42     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  92:3-94:53     warning  Missing blank line before block node                                       no-missing-blank-lines
  92:5-92:57     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  93:5-93:39     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  94:5-94:53     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  96:3-98:92     warning  Missing blank line before block node                                       no-missing-blank-lines
  96:5-96:37     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  97:5-97:46     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  98:5-98:92     warning  Don’t use literal URLs without angle brackets                              no-literal-urls
  98:5-98:92     warning  Very hard to read sentence

_content/getting-started/setting-expectations.md
   3:1-3:10  warning  Remove “There are”          there are

_content/index.md
  7:56-7:63  warning  Replace “initial” with “first”  initial

⚠ 65 warnings

[bkeepers]

I'm going to merge this now and start submitting some small PRs to fix the current warnings.