Log release ID for invalid MBIDs
Add badges of travis and coverage to README
Add irc notifications by travis
Merge pull request #635 from skeuomorf/badges

Add badges of travis and coverage to README
Merge pull request #636 from skeuomorf/notifications

Add irc notifications by travis
Modify command: ability to delete/reset an attribute (beet modify field!)
Merge pull request #638 from brilnius/ui_del_attr2

Modify command: ability to delete/reset an attribute (beet modify field!)
use the new python enum instead of hand-rolled version
add enum34 to install_requirments
Make mediafile tests independent of image order

For MP3s mutagen stores image tags in a hash with the `APIC:...` key. The order
of the images is therefore not well defined. A similar issue occurs with WMAs.
Use tox to test on travis and add docs and flake8

Travis CI now also confirm that the docs build correctly and the flake8 runs
succesfully. Tox also has the advantage that it tests that beets installs
correctly.

Currently flake8 does not run succesfully so it is configured to not fail the
build on Travis.
Ignore generated man pages
Sphinx is required to build the package
add util test file with tests for enumerations. fix super() bug
We need sphinx before installing the tox environment
Add sphinx dependency to tox virtual environment
Use coverage only with py27
import single files and one-track albums

An alternate proposal for what's being discussed in #640.
Merge pull request #643 from geigerzaehler/tox-flake8-travis

Use tox to test on travis and add docs and flake8
tox: restore pypy/py26 configs, sphinx -q (#643)