Removing TAG as a part of speech tag.

Both metanl.english and ProcessWrapper in metanl.extprocess, instead of
treating "#word" and "@word" as special unstemmed tokens with the part of
speech "TAG", will now give them the stems and parts of speech they would have
had without the leading # or @.

Also removing some unused imports from metanl.english, while I was in there.
Treat @-mentions like #-tags in metanl.english
Merge pull request #4 from commonsense/taglessness

Removing TAG as a part of speech tag.