Properly detect multi-character emoji

Implement the ability to pass a block to encode_io and encode

Previously emoji like 👨‍👨‍👦 (:man-man-boy:) were decoded as
:man::man::boy: (👨👨👦) even though there is a specific emoji entry for
:man-man-boy:. The solution is to change how the regexp is constructed.
Instead of not setting a sort order for the emoji that go into the
regexp we use reverse alphabetical order to ensure that any emoji that
are inclusive of another (such as :man-man-boy: including :man) get
sorted BEFORE the emoji that they include.

We accomplish this by using a `SortedSet` and implementing `<=>` on `Emoji`

This allows a library user to easily customize the representation of an
emoji (mapping it to a custom image for example)

added missing emoji - shooting star

Add 300+ missing Emoji

Avoid creating symbols based on user input

Without a pre-built lookup, we will look through all existing emojis (~1000) for non-existent emoji cheat codes. This is 30x faster than caching on demand in the presence of non-existent cheat codes, and roughly the same speed as caching on demand when there are no non-existent cheat codes.

The emoji landscape has changed quite a bit since its introduction

doing this should fix travis ci builds

add :simple_smile: to 😄 emoji for Slack compatibility

2014-2015 emojis (http://www.unicode.org/emoji/charts/full-emoji-list.html)

fix line brake bug

Faster encode technique

Conflicts:
	lib/rumoji/emoji/symbols.rb

Ignore arbitrary strings wrapped in colons