Add functionality for showing and adjusting bass, treble.

Move music adjustment related functionality to separate class.

Builds on and requires https://github.com/SoCo/socos/pull/14 for moving
socos.py into socos/core.py
Import print_function for backwards compatibility.
Renamed class MusicAdjustments to RenderingAdjustments.
refactor volume/bass/treble adjustment
run doctests from makefile
Adds remove 'index' command.
Added extra space between functions.
Fixed
C:299, 0: Wrong hanging indentation.
index,
   ^ (bad-continuation)
C:300, 0: Wrong hanging indentation.
queue_length)
^ (bad-continuation)
Added function remove_range_from_queue(sonos, start, stop)
(Re)-implemented speaker list sorted by ips
Merge pull request #22 from petteraas/remove_range_from_queue

Remove range from queue
Merge pull request #39 from KennethNielsen/ordered_list

(Re)-implemented speaker list sorted by ips
Merge pull request #34 from SoCo/vol-bass-treble

Add bass and treble (refactored)