Implements support for WMA/ASF

 * Adds support for importing/managing .wma and .asf files
 * Adds support for all available ASF tag equivalents
 * Adds two utility methods for (un)packing embedded ASF pictures
 * Modifies scrub plugin to work around the lack of a delete method on
   ASFTags object.
Safely cast ASFBoolAttributes

 * Modify _safe_cast to account for ASFBoolAttributes
Don't auto-tag partial matches.

Add `import: confirm_partial` setting, with a default of "no" (current
behaviour). If set to "yes", strong recommendations for partial matches will
be downgraded to medium recommendation, thus will require confirmation and
will not be auto-tagged.
Safer defaults on confirmation prompts.

Remove default option and require selection on confirmation prompts for:

- Partial matches, if `import: confirm_partial` setting is "yes".
- Matches that are below the medium recommendation threshold, but above the
  gap threshold.
- Matches that have no recommendation.
- Matches other than the best and auto-suggested match.
Align LHS and RHS changes. Put track/duration differences on RHS.
Add docs for `confirm_partial` setting.
silence Unidecode warning due to byte string info

--HG--
extra : source : 6a023b1f3ace0ae3177afb382d0eebcb445bec05
version bump and changelog summary for 1.1b1
Added tag v1.1.0-beta.1 for changeset 6f29c0f4dc70
Map a few more tags to custom/nonstandard attributes

 * Adds TotalTracks, TotalDiscs, MusicBrainz/ASIN and
 * Acoustid/Fingerpint
Add database_change event
Add cli_exit event
Add lib param to database_change event
version bump: 1.1b2
merge new events (#79)
docs for new plugin events (#79)
merge WMA support (#75)
minor style cleanup for #75
changelog/docs for WMA support (#75)
add "bogus" WMA names for nonstandard data (#75)