Support for OpenH264 codec

[bennylp]

Support for the open source implementation of H.264 codec from ​http://www.openh264.org.

Implementation features:

• Constrained Baseline, default level=30 (0x1e)
• packetization modes: 1, 0
• key frame request and indication
• obey remote's fmtp

Notes:

• currently transmission is hard coded to use only single NAL (packetization mode 0) regardless of remote's fmtp for interop reason. The same is also done in ffmpeg wrapper.
• whole frame for file encoding is implemented but currently doesn't work

Below are the steps to use the codec:

For GNU targets:

1. Run configure with --with-openh264 option specifying the directory of OpenH264 source files. E.g.:

   ./configure --with-openh264=/home/user/src/openh264-trunk
   

2. Add this to your config_site.h:

   #define PJMEDIA_HAS_OPENH264_CODEC		1
   

For Visual Studio:

1. Add this to your config_site.h:

   #define PJMEDIA_HAS_OPENH264_CODEC		1