Add skin tones support

[mislav]

This adds Emoji::Character#skin_tones? which returns true if the emoji supports Fitzpatrick skin tone modifiers (1F3FB-1F3FF).

[chvp]

Any reason this isn't merged?

[kinduff]

:+1: on this, hope this can get attention and get merged

[mislav]

@chvp Sorry for my late reply. This reason this wasn't merged is because emoji.skin_tones? on its own wasn't very useful to ship. Your application would be able to detect if an emoji supported skin tones, but not much more unless you built up the logic of parsing/inserting the Fitzpatrick modifiers yourself.

I've now added support for skin tones to Emoji.find_by_unicode and the ability to list each skin tone variant for an emoji: Emoji::Character#raw_skin_tone_variants.