Don't include hd in the info of a Google Account

hd is only available for Google Apps account (domain) so we're
better off not returning it all for now
Add ability to delete a playlist
Refactor: separate module for Playlist methods

Let's try to keep files short and readable
Refactor: separate module for Subscription methods

Let's try to keep files short and readable
Add ability to unsubscribe from a channel

This commit also improves the subscription tests and code so we
are actually unsubscribing from a channel before testing that we
can subscribe, and the other way around.
Remove Travis matrix to avoid test conflicts

If you run tests in parallel on Travis, then one test might destroy
the subscription that the other test just built, causing tests to
fail.

If you do want a matrix of test suites, we need different credentials
for each one of them
Add ability to add/remove playlist / items

Although some methods to handle playlists were already present,
this commit makes them more coherent by adding separate modules
to deal with whole playlists (create, find, delete) and to deal
with playlist items (add, remove).

The prototype of find_or_create_playlists changes, and the yield
is dropped because it was confusing and not really used.
Add ability to update a playlist
Bump to version 0.3.0