Audio win 24bit - BufferDynamic types for Interleaved, Spectral

This addresses the lack of 24-bit PCM decoding support on windows, discovered by @sansumbrella in [this form post](https://forum.libcinder.org/topic/wav-file-playback-on-windows-7).  I also added 24-bit encoding support for `TargetFileMediaFoundation`.

In order to not make the copying during decode too expensive, I needed to rework `BufferDynamicT` to allow for other variants, so now there are typedefs for:

* BufferDynamic - the default, contigious channels. Used all over the place.
* BufferDynamicInterleaved - only used on windows
* BufferDynamicSpectral - not used anywhere.... yet

Since this is a substantial change to a core component, I'm going to wait until I have made sure there are no regressions in tests / samples before merging this.