__version__ for __mappy__

[jbloom]

Would it be possible to add a __version__ string (e.g., mappy.__version__)? This is the standard way of accessing version numbers for Python modules / packages:
https://www.python.org/dev/peps/pep-0396/

This would facilitate writing larger Python packages that use mappy as a dependency.

[lh3]

Could you send a pull request? Thanks.

[1pakch]

I can expose a version from here

minimap2/main.c

Line 13 in 154d2ca

#define MM_VERSION "2.10-r784-dirty"

as a LooseVersion as per PEP-386.

I am not sure how well this versioning scheme would integrate with the Python packaging ecosystem though.