Added LocalCorpus.delete() method, as an opposite to LocalCorpus.save().


git-svn-id: http://music21.googlecode.com/svn/trunk@3659 5c16147e-a200-11de-b0cc-ab0ad15e60d0
Improved corpus documentation.

git-svn-id: http://music21.googlecode.com/svn/trunk@3660 5c16147e-a200-11de-b0cc-ab0ad15e60d0