enh: augment string parameter for algorithms by optional dict of kwargs
fix switch_to test.
Also, don't switch back after switching.
absolute URL for scikit-learn in README
reorganize some tests (sort by learning algorithms tested)
Merge pull request #30 from larsmans/sklearn-url

Absolute URL for scikit-learn in README
FIX TST make subgradient latent ssvm test more stable
more idiomatic abstract methods

The even more idiomatic way is to use ABCs, but those work differently
in Py2 and Py3, and I wasn't sure if PyStruct targets 3.x
DOC shape=(model.size_psi,), not (model.psi,)