0.5.1

This is the first bugfix release of the 0.5 series.

In comparison with 0.5.0, we have changed the default classifier: it is no longer TaxoNet but "flat multitask". In doing so, we revert to the species classifier that was already present in BirdVoxDetect 0.3.0. We have made this change because we have noticed a surprisingly poor performance of TaxoNet on hold-out data. Thus, we err on the side of caution and offer a more straightforward deep learning model as the new default. We are currently investigating the cause of the problem in coordination with BirdVoxClassify developers.