Declare a __version__ constant for future use
Declare a __version__ constant for future use

This will be used by setup.py and a devel/release script, as well as an
`augur version` command.

We want to start versioning augur beginning with 3.0.0.  While preparing
for the final 3.0.0 release, we'll use development versions (.devN), as
described in <https://www.python.org/dev/peps/pep-0440/#developmental-releases>.

nextstrain/augur,nextstrain/augur,nextstrain/augur,blab/nextstrain-augur