audo bug fixes

Ignore-this: 8d5635fa8350e5e7f1bf3aee966c5713

1. fixed decimate and inflate to work with more than one channel
2. simplified code by using casts to short arrays
3. added simple low pass filter

darcs-hash:20140712050546-c21fe-0b8fd635583b03b27144bcff2b0dd4a27defac37
changed to 12kh audio

Ignore-this: 36954b95254310efda4bf5361861763e

darcs-hash:20140712052111-c21fe-eb379b8e4ab8adb18ea1a95f7a451fde715882a1
added libopus to cmake for mac

Ignore-this: 8c8690634b40b946c629b4a19eb01ddf

darcs-hash:20140712052554-c21fe-9331c48c32fbe3fa45694509350a1bcdaf676b34