Updates to opus build.

* Build celt, silk_common, silk_fixed, and silk_float libraries.
* Update celt/silk_common/silk_fixed/silk_float solutions to be XP-compatible (v120_xp, subsystem windows, 5.01/5.02) and use MD/MDd instead of MT/MTd.
* Header fix to opusfile.h to include opus_multistream.h via relative path.
* Update build script to copy all the libraries.
Copy MSVC debug runtime DLLs into lib dir for debug environments.
Link celt, silk_common, silk_float, and silk_fixed directly into opus.lib.

* Enable link library dependencies for Opus.
* Add project references for opus (and set those to link library dependencies).