Load COL_SCHEMEs from files

[baskervald]

Rather than having ui/__main__.py need to be edited for users to add their own color styles, users can now add their colorschemes using .col files within $XDG_CONFIG_HOME/hangups/colors using this format:

(just a translation of the solarized-dark colorscheme to the format)

active_tab     'light gray' 'light blue'
inactive_tab   'underline'  'light green'
msg_date       'dark cyan'  ''
msg_sender     'dark blue'  ''
msg_text       ''           ''
status_line    'standout'   ''
tab_background 'underline'  'black'

Comments can be added if they're prefaced with #, and the spacing is unnecessary but more readable.

[tdryer]

Nice idea! I'm not sold on the custom file format though. What do you think of this method?

1. Allow specifying colours in the arguments and config file, for example --col-active_tab "light gray". This keeps consistency with how the other options work.
2. To support colour scheme files, use an approach similar to what you've done here, but load the file using ConfigArgParse again, so it can use the same format.

We'll also need to update the documentation.

[tdryer]

After writing that I remembered about the foreground/background issue, which would make the arguments messier. Maybe it's simpler to just keep colour schemes separate. I'll have to think about it.

[baskervald]

Yeah. I was initially thinking of using the config format already in place, but I realized that it'd be really difficult to use for two values, especially since commas are already taken for having mutliple values in foreground (or background). ex. "underline,light blue", so I decided on a shlex-based format which has the easiest time processing multiple values.

[tdryer]

How about JSON? Slightly verbose, but it's also more self-documenting.

{
    "active_tab": {
        "foreground": "light gray",
        "background": "light blue"
    },
    ...
}

[baskervald]

That's definitely an option. I didn't go with that due to my dislike for how verbose it is, but I'll throw together a branch that uses it real quick.