Add compact_output option

[rinpatch]

As discussed in
#393 (comment).
I did not name the option "single_line", since newlines in code blocks
are preserved even with it on and since Earmark passes
the single newlines from the input to the final output.

Also removes some string concatenations and replaces single-character
binaries with character codes.

I did not find a file the tests for this feature would fit in, so
I created a new one at test/acceptance/html/compact_output_test.exs

Closes #391

[RobertDober]

Ty for your work, appreciated I will plan a release within the week

[RobertDober]

@rinpatch scratch the last remark, I have 10 failing tests after the merge (but only locally Travis is still happy) I have to check that out first

[RobertDober]

So here is the problem I am having

Interactive Elixir (1.11.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> Earmark.as_html("[link](/uri \"title\") [link](/uri \"title\")")
{:ok,
 "<p>\n<a href=\"/uri\" title=\"title\">link</a><a href=\"/uri\" title=\"title\">link</a></p>\n",
 []}

There is not a space anymore between the two links which is clearly needed, hopefully I can fix this but I will do so in a side branch and revert the merge, sorry!

BTW. Still no idea why Travis does not catch these errors, you should see them locally too

here is the corresponding test

mix test test/acceptance/html/links_images/titles_test.exs:5                                                                                                     [14:33:07]
Excluding tags: [:test]
Including tags: [line: "5"]



  1) test Links with titles two titled links (Acceptance.Html.LinksImages.TitlesTest)
     test/acceptance/html/links_images/titles_test.exs:5
     Assertion with == failed
     code:  assert as_html(markdown) == {:ok, html, messages}
     left:  {:ok, "<p>\n<a href=\"/uri\" title=\"title\">link</a><a href=\"/uri\" title=\"title\">link</a></p>\n", []}
     right: {:ok, "<p>\n<a href=\"/uri\" title=\"title\">link</a> <a href=\"/uri\" title=\"title\">link</a></p>\n", []}
     stacktrace:
       test/acceptance/html/links_images/titles_test.exs:11: (test)



Finished in 0.08 seconds
2 tests, 1 failure, 1 excluded

Randomized with seed 667380
```

[RobertDober]

@rinpatch your patch is fine this is just a strange hiccup I have to sort out sorry for the delay, please stand by.

[RobertDober]

@rinpatch I managed to clean up the mess on my local machines, and just released v1.4.12 which, of course, contains your PR again

Well done and thank you

[tmjoen]

This is great! I have been on 1.4.4 for a while now due to the whitespace changes, but this passed all my tests except one:

iex(1)> Earmark.as_html!("<div class=\"lead\">**Some** text here.</div>")
"<div class=\"lead\">\n  **Some** text here.</div>\n"
iex(2)> Earmark.as_html!("<div class=\"lead\">**Some** text here.</div>", compact_output: true)
"<div class=\"lead\">  **Some** text here.</div>"

There seems to be 2 extra spaces inserted in nr 2 there :)

[RobertDober]

@tmjoen can you please open an issue too late, I have already fixed it

[RobertDober]

... and released 1.4.13

[tmjoen]

Haha, thanks @RobertDober ! You're too fast for me 😅