Changes

MessageBuilder update
* Changed some append methods to support all CharSequences
* Added replace methods
* Added stripMentions(MentionType...)
* Added a shortcut to strip all mentions
* Added a getter for the StringBuilder
* Made format pattern static final and mention pattern protected
* Added indexOf and lastIndexOf
* Added append(IMentionable), append(String) and append(String,
Formatting...).
* Deprecated append[...]Mention() and appendString() methods
* Added isEmpty() and renamed getLength() to length()
* Added append(Object)
 (commit: 00379c8)