Update genres-tree.yaml

Scraped https://en.wikipedia.org/wiki/List_of_popular_music_genres for the first time since @KraYmer did back in (apparently) October 2011. This should be much more useful now to those who have genre canonicalization enabled. Script is in public repo of mine :)
Alphabetize! Thanks @KraYmer
added an option to make the playlists created by play plugin to be
relative to a path much like the smart playlist plugin
updated documentation for play plugin adding relative_to option info
Merge pull request #931 from BrainDamage/playrelative

play plugin can generate relative paths
Changelog for #931
info: Show data for each item, not only first one
Update genres-tree.yaml
Refactor cli main function

The logic of setting up beets and running a command was scattered
across the `_raw_main` and `_configure` functions. This is an attempt
to bring more structure to the process and to diminish the dependency
on global state.
Increase test speed by removing unnecessary file operations
Refactor _load_plugins

Move configuration validation into `confit`. Get rid of dependency on
global configuration object.
PEP8 Fixes
Bump version in setup.py

see 787f0e25c529043201d8397250c542a5c0d6f479
Quieter Travis notifications in IRC
Change expected result for compatibility with updated genres-tree.yaml
Failing tests for empty import directories

Reproduces #932.
Add ImportTaskFactory class

Removes duplication and makes code leaner. Also fixes #932.
Merge remote-tracking branch 'origin/patch-2' into patch-1
Correct busted encoding hopefully
Remove duplicate OrderedEnum and use utils instead

This is a leftover cleanup from c4e6f389.