tests missing in pypi sdist

[dvzrv]

Hi! When starting to package 0.2.0 for Arch Linux to be able to run tests for doit I have noticed that the pypi sdist tarballs do not have the tests.
Could you please add them? The pypi sdist tarballs are quite frequently used by downstreams as pypi.org offers more access to uniquely named tarballs.
The github tarballs are fine too, but usually it's nice to have tests anywhere where people are building from source.