2.1 beta release

Refined mention detection, added an option to add a code buton in the
editor automatically, worked on aesthetics in the plugin info menus and
reworked the force enable all mention alerts script to give standard ACP
error messages rather than simply redirecting 'silently'.
Addressing #18

Padding requirements changed and I forgot to update the code.
Addressing #19

Incorrectly changes the position of the global $cache statement and
caused an error. It has been fixed.
Addressing #20

Added support for single quotes and ` characters to be used to surround
user names in the quoted syntax.
Merge pull request #23 from WildcardSearch/feature

MentionMe 2.1 Release