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

fix colon with emoji problem

This is a fix for #7.
In addition to the updated iterator, I've adjusted the numeric emoji to
use accurate unicode codepoints.

Make decode regex work with codes that have dashes in them

Handle some edge cases with "possible emoji"