Packaging the tests, or not

[dimbleby]

Fixes #281, #282

• first commit explicitly excludes tests from the binary distribution, it is indeed unconventional to include them
• second commit explicitly re-adds them to the source distribution
  • I don't think there's universal consensus about whether this is desirable or not eg here is a recent discussion
  • but it seems harmless and seeing as how No tests in pypi sdist tarball #281 explicitly asks for them, well why not?

[itamarst]

This would enable re-releasing the yanked .12 release, seems like a good idea.

[itamarst]

Any chance this can be merged and a new release made? Thanks!

[KOLANICH]

Thanks for fixing that.