Implementing set-interface on metadata.MetadataBundle.

Removed MetadataBundle.updateAccessPaths(); use MetadataBundle.validate()
instead.


git-svn-id: http://music21.googlecode.com/svn/trunk@3578 5c16147e-a200-11de-b0cc-ab0ad15e60d0
Added more set-interface methods to metadata.MetadataBundle.

MetadataBundle now implements the following set-interface methods:

    __and__
    __ge__
    __gt__
    __le__
    __lt__
    __or__
    __sub__
    __xor__
    difference
    intersection
    isdisjoint
    issubset
    issuperset
    symmetric_differnence
    union

Tests are forthcoming.


git-svn-id: http://music21.googlecode.com/svn/trunk@3579 5c16147e-a200-11de-b0cc-ab0ad15e60d0
Wrote docstrings for MetadataBundle.__and__, __or__, __sub__ and __xor__.

git-svn-id: http://music21.googlecode.com/svn/trunk@3580 5c16147e-a200-11de-b0cc-ab0ad15e60d0