Add WASAPI audio capture

 - Add WASAPI audio capture for windows, input and output

 - Check for null pointer in os_dlopen

 - Add exception-safe 'WinHandle' and 'CoTaskMemPtr' helper classes that
   will automatically call CloseHandle on handles and call CoTaskMemFree
   on certain types of memory returned from windows functions

 - Changed the wide <-> MBS/UTF8 conversion functions so that you use
   buffers (like these functions are *supposed* to behave), and changed
   the ones that allocate to a different naming scheme to be safe
CoreAudio: Separate enumeration code

The enumeration code being up at the top was making things quite messy,
so I split that code out to a separate set of files.