Changed domain arguments to music.spectrum() to member variables of
music.Estimator, since the region on R2 over which an array is useful is
a static property of the array. This simplifies the music.spectrum()
argument list substantially.
Tests now properly call the new music.Estimator initializer and
music.spectrum().
Implemented parallel computation of the spectrum, and incidentally
monkeypatched away the orientation issue (inverted DoA).
Support timetrial test and generating differently sized spectral plots
with spectrum test command.
Merge branch 'timetrial' into parallel_spectrum, so that the parallel
implementation can be properly compared to the single-threaded.