utils: Add review note to EventEmitter.call()
utils: Remove redundant list comprehension
init: Hide internals from module object
session: Use to_char_or_null() helper
Remove multiple extra sp_link_add_ref calls

Creating links from URI string, Image, Search, Track, and User objects called
sp_link_add_ref() an extra time, causing the sp_link objects to never reach a
refcount of 0, and thus a memory leak inside libspotify.
docs: Update changelog and dev plans
docs: OS X (at least with X Code) includes libffi
Use to_unicode_or_none() helper
Use to_char() and to_char_or_null() helper
Be explicit about add_ref or not
playlist: Check error on playlist.add_tracks()
session: Replace some to_char_or_null() with to_char()
Keep lock while reading data from libspotify

If a libspotify function is called by another thread before we read data out of
the pointers returned from libspotify, then the data may be changed and we may
be working on freed data, which would be very bad.

Thus we keep the global lock until we've copied the string to Python space, or
in the case of sp_* pointers, we keep the lock until we've called sp_*_add_ref
on the pointers.
docs: Update changelog
docs: Fix syntax
docs: Comment hacks
init: Add __wrapped__ to decorators also on Python <3.2
docs: Undecorate methods so Sphinx can inspect signatures
docs: Fix reference
docs: Make docs build on Python 3