Replace vendored emoji.json w/ official Unicode .txt files

[jeffweiss]

As @mroth mentioned in #5, he'd like to eventually replace the vendored emoji.json file with the official Unicode text files.

Possibly from a combination of

• http://www.unicode.org/Public/emoji/latest/emoji-data.txt
• http://www.unicode.org/Public/emoji/latest/emoji-sequences.txt
• http://www.unicode.org/Public/UCD/latest/ucd/EmojiSources.txt
• http://www.unicode.org/Public/UCD/latest/ucd/NamesList.txt

[mroth]

Just as a FYI on this, it's worth noting there is a fair amount happening "upstream" in the Ruby version of this library which would have to be reconciled with whatever happens here: https://github.com/mroth/emoji_data.rb/pulls

Would love your thoughts!