bmdplay: prevent a deadlock
bmdcapture: explicitly stop the streams

Should be safer and cleaner.
bmdcapture: remove leftover code

We are not encoding in the capture.
bmdcapture: simplify the write loop

Valgrind seems confused enough to not report the free.
(tested replacing the destructor with a chatty one)
bmdcapture: count the output frames
Merge branch 'master' of https://github.com/lu-zero/bmdtools