Update MANIFEST.in

[astamminger]

Updated the MANIFEST.in file to include the LICENSE file with the source package and replaced the explicit inclusion of the test file with a recursive include for the complete tests folder.

Fixes #22

Although the conda-forge recipe for the click-spinner package already existed for some time (click-spinner-feedstock) these changes to the MANIFEST.in would make the release process of future versions less error prone. (Mentioning @ltalirz for reference)

[ltalirz]

Thanks a lot @astamminger !
So nice if I postpone working on something and a few hours later discover somebody else already solved it for me. Perhaps I should do this more often ;-D

[ltalirz]

Pinging @yoavram as well

[yoavram]

thanks!