Visualise Music 0.1.1

Fixes a build that could fail with every file in the library reported as "could
not be analysed".

The analysis compiles part of librosa to native code the first time it runs.
Letting every worker do that at once produced faulting code on some processors,
and one worker dying failed every file the pool was holding - so a single crash
arrived as a list naming files nothing had touched. The analysis now compiles
once, before the workers start. When a pool does die it is reported once, as
itself, rather than blamed on the audio.

Two things that made that hard to see are fixed as well: a failed run named a
log directory that did not exist, and the second half of a build overwrote the
first half's log.

Also new: ctrl-Z and ctrl-Y walk back and forward through what you have played,
panning the map to each sample rather than only replaying it.