This diff adds mbedTLS support to the obs-outputs plugin. PolarSSL and
mbedTLS have grown so different between 2015-or-so when libRTMP was
written, and now it's no longer feasible to just use the USE_POLARSSL
flag.
This commit adds a WITH_RTMPS tri-state CMake variable (auto/on/off),
set to "Auto" by default. "Auto" will use RTMPS if mbedTLS is found,
otherwise will disable RTMPS. "On" will make it require mbedTLS,
otherwise fails configuration, and "Off" disables RTMPS support
altogether.
Closesobsproject/obs-studio#1360
Note that this is a somewhat heavily modified custom version of librtmp.
I modified all the platform specific code that we were using for the
OBS1 to make it platform-independent.
I don't really like the code in this library, but it works well enough,
so I can't really fault anyone for it. It's just very.. unclean. Even
for a C library, quite unclean. Some parts are also a little less safe
than I'd prefer as well.
