new shield_list customization option

[buhman]

I originally just wanted support for a circleci button, then I realized this could be made much more generic.

This adds support for including arbitrary shields in the about section.

Usage:

html_theme_options = {
    'shield_list': [
        {
            'image': 'https://img.shields.io/circleci/project/github/RedSparr0w/node-csgo-parser.svg',
            'target': 'https://circleci.com/gh/RedSparr0w/node-csgo-parser'
        }
    ]
}

[polyzen]

Looks good to me.

[bitprophet]

Nice, thanks! Related / possibly subsumed in this: #13, #52.

Minor nitpicks:

• we don't use circleci ourselves last I checked, so using it in the example snippet feels funny - I'd switch it to reference codecov or travis or something maybe?
• which brings one to: this should arguably replace/deprecate the standalone options for travis and codecov. Can't actually replace til a later release, but we should least list this above those two, and add note/warn blocks to those two saying "you should probably use shield_list instead".

Also wondered if we could roll the GH button into this too, but it seems to use different HTML so meh, no big deal. (GH also has other options as well, so, it's special.)

[buhman]

this should arguably replace/deprecate the standalone options for travis and codecov

I agree.

we don't use circleci ourselves last I checked

Yep; I didn't want to passive-aggressively suggest that shield_list should replace travis_button without actually establishing that first.

[buhman]

@bitprophet I changed the example to something that actually exists.

[sloria]

This is almost identical to #124 . The only difference is that #124 uses a different option name (badges) and allows width, height, and alt. It doesn't have the docs re: deprecation, though. FWIW, I think badges is a better name name than shield_list because it is more service-agnostic and therefore more future-proof (could easily switch to badgen and the option name would still make sense).

@bitprophet I recommend going with either this or #124 and closing the other.