Removed undocumented method MidiFile.get_messages().
Added bpm2tempo() and tempo2bpm() to lib.rst.
Added merge_tracks().
mido-play now uses tempo2bpm() and prints BPM with fewer decimals.
Removed note about sleep=False from MidiFile.play() doc string.

It was removed before release when __iter__() was added, so is now obsolete.
Moved changelog to docs/changes.rst.
Updated changelog.
Converted a couple of list comprehensions into generator comprehensions.
Bugfix: receive() checked self.callback which doesn't exist for all ports.
Moved changelog up to the top of the index.
Raises IOError if you try to open a virtual port with PortMIDI.

(They are not supported by this backend.)
Pygame also raises IOError when you try to open a virtual port.
Updated reference to changelog in readme and removed CHANGELOG.rst.
Added section about virtual ports to docs.
Updated docs.
Updated some error messages.
Updated changelog.
Bumped version to 1.1.12.