playlist: Change reorder_tracks() to use track positions.

Fixes #134
Merge pull request #136 from kingosticks/fix/reorder-tracks-using-positions

Change reorder_tracks() to use track positions.
docs: Update authors
docs: Remove OS X pyspotify installation warning

I've just tested the following combinations:

- OS X 10.9.3, Xcode 5.1.1, Apple Python 2.7.5: OK without workaround
- OS X 10.9.3, Xcode 5.1.1, Homebrew Python 2.7.7_2: OK without workaround

Thus, I'm removing the warning from the docs.
docs: Detail how to install pyalsaaudio and pyaudio
docs: Include workaround for #130
Add line parameter to shell.py methods

Commander sends two arguments to each method, so they fail when they
only have one parameter.