rosetta-code.metronome, simplify and fix script/deploy

Timers have 1 thread per timer, so it's ok to block. This removes
the need for a timer releasing a semaphore and another thread
acquiring the semaphore.

Also, when running in with-ui, the quotation must return for the UI
to actually start, so the previous method didn't work
with-ui docs, clearly state that the quot must return
rosetta-code.metronome: parse command line
rosetta-code.metronome: usage, validation