Added GNU/Linux support to play() function

Firstly, thank you for this project and a great talk at Pycon. I've been working on Sator, a project for analyzing atonal music that you might find interesting: http://sator.readthedocs.org/

I'd like to help work on adding support for GNU/Linux for midi output. The approach I've taken here is just to call Timidity directly, because use of subprocess.call(['open', f.name]) fails with "Couldn't get a file descriptor referring to the console" on GNU/Linux.

I think some other approaches are possible, but I'm not sure what would be the most preferable. Also, Timidity seems to be the usual program for MIDI support on GNU/Linux but of course there are likely others. Would it be worthwhile to add an optional kwarg to the function for this argument? (such as passing program_name='timidity')

Let me know any thoughts and I'm happy to amend these changes