Initial commit of FLTP format binkaudio support.  Converts to FLT format by manually interleaving decoded samples.  swresample library is included with a view to use swr_convert() in future versions, but not used in this commit.
Minor cleanup.  Tested successfully on windows x64 using ffmpeg-20140823-git-7444cf9-win64-dev which is on libavcodec version 56.0.101.
Working version - converts FLTP to FLT.  Does not work when converting to S16.
Now works for both FLT and S16 formats.  The output format is hard coded in the MovieAudioDecoder constructor (default S16).
Cleanup comments.
Implemented feedback review comments, removing hard coded values and adding error handling.
More cleanup.
Simplify the use of swr_convert and add #ifdef guards around code that require libswresample.
Attempt to work around travis.
Minimize the use of #ifdef guards for better code legibility.
Make travis happy again.
More refactoring, remove more #ifdef guards and fix repeat samples for planar formats.
Moved format conversion to audio_decode_frame()
Support for ubuntu/debian.  Can easily be reverted if not required.
Make cmake more reliably detect libswresample
Arrgh... silly typo
Code review fix.
More fix based on code review.
Remove incomplete implementation to support planar formats.  Make libswresample a prerequisite.
Add libavresample support.  Tested on windows x64 only.