Add +git suffix to the VERSION macro, to reflect ongoing development

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Add support for removing tags from a file (-d)

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Add support for stripping all tags from a file (-S)

This includes stripping out specific tag implementations from files,
that support more than one such implementation to exist (like mp3s).

The write-map is used as with other write operations. So, to strip
an id3v1 tag-block from an mp3 file, you'd do this:

  % taggit -W mp3=id3v1 foo-bar.mp3

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
taggit_tag: Hand in a reference to the file structure

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Don't let -d add tag implementations

Before, when you did:

  % taggit -W mp3=id3v1,id3v2,apetag -d album foo.mp3

Would add an (albeit empty) ‘apetag’ block to "foo.mp3" if it didn't
have one before. This is a little counter-intuitive.

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>
Fix uncaught exception with broken map definitions

Signed-off-by: Frank Terbeck <ft@bewatermyfriend.org>