Increase version.

Update github actions to check PR branch.

Merge pull request #2 from tatsy/dev

v0.2.2
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* Change Python env manager to Pipenv.
* Add methods computing approximated Laplacian-Beltrami operators (adjacent, cotangent, Belkin+2008).
* Add IPython notebooks as Pythons examples rather than simple scripts.
* Change traversal order of elements around a vertex to counter-clockwise order.
* Add heat kernel signature [Sun et al. 2009].

Minor update.

Update README.md, and increase library version.

Minor update.