raw pcm input

I have restructured the audio input framework for the Aften commandline program. There is now a separate directory (and static lib) for processing audio input. The major reason for this change was to support raw pcm input. The new framework will also make it easier to add support for other audio formats.

With this change are 3 new commandline options.

[-raw_fmt X]   Raw audio input sample format (default: s16_le)
                   One of the pre-defined sample formats:
                   u8, s16_le, s16_be, s20_le, s20_be, s24_le, s24_be,
                   s32_le, s32_be, float_le, float_be, double_le,
                   double_be
[-raw_sr #]    Raw audio input sample rate (default: 48000)
[-raw_ch #]    Raw audio input channels (default: 2)