Add version number to module

fix #19
Better support for fetching stickers from MPD

MPDClient now parses the output of MPD and provide a more convenient way
of accessing stickers.
stickers: add test for special case for parsing stickers output
doc: provides a new porting doc to explain API breakage
Merge pull request #20 from multani/better-stickers-support

Better support for fetching stickers from MPD
Rewrite Readme in Restructured Text
Restructured Text: github-friendly file ending
Increment version number to 0.5.0
Merge remote-tracking branch 'upstream/master'
Some minor corrections in README.rst; set correct VERSION in mpd.py

- mpd.VERSION was not updated to (0, 5, 0)
- removed a meaningless "instead" in the README
- the newest unmasked version of python-mpd in gentoo now also points to
  this fork