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Fixes #49 #52

Specifically, about what the compatibility and kernel parameters are, about missing the weights, and some pointers about learning.

There was a sudden interest in this, both via issues (#23) and direct e-mail almost simultaneously. Odd 😄

Especially, installs `__init__.py` which is necessary for the import.

Fixed transposed pairwise feature size in README, and noted that feature dimensionality is not necessarily equal to number of labels.