Update my ports to be compliant with new USES framework and fix other issues.
* various: migrate USE_BZIP2 to USES=tar:bzip2
* various: migrate USE_XZ to USES=tar:xz
* multimedia/py-ffmpeg: add and prefer github (GH) as master site
* ports-mgmt/portbuilder: specify license as BSD2CLAUSE (instead of just BSD)
Most ports are updated infrequently so a single batch commit is preferred over
collating changes per port.