Add option to skip filetype-specific colors (again)

[DarkWiiPlayer]

Same as #119 but without indentation for easier diffing :)

[pickfire]

@DarkWiiPlayer Creativity +1 😆 👍

[DarkWiiPlayer]

*poke*

[NLKNguyen]

Hi,

Sorry for the late response, I didn't forget this. I originally planned to implement this feature in a different way but never got time to do so. I guess I can do it after Thanksgiving :).

Here are the reasons:

First of all, it's not advised to introduce the usage of an arbitrary global variable. I try to keep all options as key/value pairs within 1 single global variable for PaperColor: g:PaperColor_Theme_Options (see the README usage). And there is a mechanism in which the option only affects an intended scope, either only a variant (dark/light) or both variants of a theme whether it is the default PaperColor or some other theme; yes, it's possible to have multiple themes on PaperColor -- I didn't advertise this feature enough but here is an example in case you wonder https://github.com/NLKNguyen/papercolor-blue ).

What I have in mind is to introduce an option, say highlight_only_standard_groups or something. Every option defaults to 0, and users can set to 1 to enable what this PR intended to do. For example,

let g:PaperColor_Theme_Options = {
  \   'theme': {
  \     'default': {
  \       'highlight_only_standard_groups': 1
  \     }
  \   }
  \ }

In case you wonder how to do add the option

In the code, you see this. It's where you can introduce a new theme option.

fun! s:generate_theme_option_variables()
  " 0. All possible theme option names must be registered here
  let l:available_theme_options = [
        \ 'allow_bold', 
        \ 'allow_italic', 
        \ 'transparent_background',
        \ 'highlight_only_standard_groups',
        \ ]

A script variable will automatically be created as s:themeOpt_highlight_only_standard_groups, and it has the value of either 1 or 0 according to the config as expected.

Second, instead of having a big if-block like the PR, that function can be terminated right after the standard highlighting groups and be done.

if s:themeOpt_highlight_only_standard_groups == 1
  return
endif

Hope this helps. I'll implement this the next time I set up Vim again. Or if you implement as I suggested and test, then I can pull. Thanks!