Remove compiler warnings
Remove the unused function WelsSleep

Windows Phone 8 doesn't have Sleep(), but there's no need to
use the function at all.
Use more modern versions of functions that don't exist on Windows Phone
Use the Windows Runtime ThreadPool API for creating threads on Windows Phone

Windows Phone lacks the old CreateThread/beginthreadex APIs for
creating threads. (Technically, the functions still do exist,
but they aren't officially supported and aren't visible in the
headers when targeting Windows Phone.)

Building code that uses the Windows Runtime language extensions
requires building with the -ZW option.
Remove the now unused MT_ENABLE define from project files
Merge pull request #614 from mstorsjo/remove-unused-define

Remove the now unused MT_ENABLE define from project files
Merge pull request #610 from mstorsjo/wp8-threads

Make threading work on windows phone
Merge pull request #598 from varunbpatil/compiler_warnings

Remove compiler warnings
Merge remote-tracking branch 'upstream/master' into travis.android