Fixed recognition of Twitch emotes.

Fixes #37. There were several problems with the old code:
1) "\b" in a Java string literal is an escape character for "backspace." Use "\\b" for RegEx word boundaries.
2) "\b" already matches line-beginning and line-end positions, so extra checks against "^" and "$" were not necessary.
3) Twitch chat only does boundary checks for emotes that do not start or end with a symbol. Emotes like "<3", ":D", etc, can appear in any part of the string. Moreover, "\\b" does not match the place where these symbols start/end because they are not "words" from regex perspective -- that's why these emotes did not get recognized at all, except when on a line by itself.

All of these issues have been fixed.