Smarter cover detection
Fix type errors in cover detection

str.startswith() and str.endswith() only accept tuples, not lists.
Allow multiple artists in metadata

Previously, xesam:artist was set to a nested list:
  [['U2', 'Green Day']]
Include all artists in notifications
Merge pull request #30 from grawity/fixes

Fix cover detection & multiple artists (for #29)
Change README to a symlink, to avoid duplicate files

The content of README and README.md *always* gets desynced.
Merge pull request #32 from grawity/readme-symlink

Change README to a symlink, to avoid duplicate files
Minor changes

 - The 'types' module is only there for "historical cases and obscure
   stuff", and should not be used in practice. Changed to the real type
   object. <http://docs.python.org/2/library/types.html#module-types>

 - Usage of `==` vs `is`. Comparing integers with `is 4` isn't
   guaranteed to always work.

 - Consistent use of whitespace in 'def ...'

 - In main(), rename `path` to `music_dir` for clarity.

 - In main(), put all config readers in one place.
Separate cover search code into its own function

Also make it handle multiple artists.
Clean up format_metadata()

mpd never returns field names that would be valid in MPRISv2, so there's
no need for the complex "remove surplus tags" code – just copy known
fields into an empty dict.
Accept non-file:// URLs for music library path

mpDris2 won't be able to use those URLs, but MPRIS clients might still
use them – for example, if the music library can be reached over HTTP.
Support LoopStatus=Track
Fix misspelled method name
build: update INSTALL from autoconf
Use idle mode instead of polling

This makes instant updates possible with very low polling frequency (10,
15 or even 30 seconds).
Cache mpd status for 2 seconds, when many properties are being queried

Since it takes three commands now (noidle, status, idle) instead of one.
Merge pull request #33 from grawity/idle

Implement "idle" mode instead of polling
Follow PEP8 for coding style
Update authors
Don't use any polling when idle mode is used