fix stub method
Muxers must be streamed by default
call setup when building an Encoder from cdata
encode names in utf-8 before to enter ffmpeg.

Names must be C-strings, thus char*s.
bootstrap the Muxer tests.
require codec cdata from outside in Encoders.
test the media_type presence
fix the missing bits for write support.
more muxer tests
reorganize the IOBridge RW handling