0.5.1 release

In the 0.5.1 release the package description was corrected in addition to the changes in the 0.5.0 release:

A decent refactoring was carried out by splitting the individual oversamplers to separate files.
SYMPROD added as the 86th oversampler implemented, thanks to @intouchkun
An experimental feature: metric learning to determine the metric to be used for neighborhood estimation added to 69 oversamplers.
A sample notebook to illustrate metric learning backed oversampling was added.
Support and CI pipelines for Python 3.9 and 3.10 added.