More Configurable Twitter Plugin (definable prefixes and suffixes)

With this revision, the user will be prompted to specify an optional prefix or suffix (such as an @user and custom hashtag) when enabling the twitter plugin. That information will be stored in the config.yml file.
Adding the #lolcommits hashtag would no longer be default if this revision is accepted as is, but could be easily tweaked into the revision.
I have never used Rake, and so I unfortunately was not able to write any test cases. This should be done before revisions are accepted. I did, however, test the following scenarios:
 - user specifies both a prefix and a suffix, tweet (with appendages) is short enough to tweet.
 - user specifies both a prefix and a suffix, tweet (with appendages) is too long and must be auto-truncated.
 - user specifies neither a prefix nor suffix, tweet (with appendages) is short enough to tweet.
 - user specifies neither a prefix nor suffix, tweet (with appendages) is too long and must be auto-truncated.
 - user has the old style of config.yml file, which does not provide prefix or suffix.