[WIP] Support Twemoji v12.0

[JuanitoFatas]

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Working Pull Request in order to keep up with Twemoji upstream.

The first step is to have all the names from Unicode data.

When this work is done, archive https://github.com/jollygoodcode/emoji-keywords, which was a scrappy solution looking at now 🤦‍♂

• parse emoji-test.txt, annotation from CLDR

  rake db:dump > db/unicode-12.0-cldr-35.1/unicode_emojis.json
  

  Parsed 3836 emojis from CLDR release-35-1!

  The Twemoji library offers support for 3,075 emojis.
  -- https://github.com/twitter/twemoji/blob/1c19734572b2d7a0f1c75ebb35e8c63fc92265b4/README.md

• 3836 v.s. 3075 🤔 !!?

• investigate emoji zwj sequences

• investigate emoji sequences

• investigate emoji keywords

• investigate emoji-variation-sequences

• Generate db/twemoji-svg.json db/twemoji-png.json from unicode_emojis.json

• Introduce new APIs for v12

• Deprecare old APIs

• Changelog entry

• Release!

Unicode 12.0 data: https://unicode.org/Public/emoji/12.0/
CLDR 35.1: http://unicode.org/Public/cldr/35.1/

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ED-17a. qualified emoji character — An emoji character in a string that (a) has default emoji presentation or (b) is the first character in an emoji modifier sequence or (c) is not a default emoji presentation character, but is the first character in an emoji presentation sequence.

ED-18. fully-qualified emoji — A qualified emoji character, or an emoji sequence in which each emoji character is qualified.

ED-18a. minimally-qualified emoji — An emoji sequence in which the first character is qualified but the sequence is not fully qualified.

ED-19. unqualified emoji — An emoji that is neither fully-qualified nor minimally qualified.

http://www.unicode.org/reports/tr51/tr51-16.html