[MRG+1] Include additional files in sdists

[toddrme2178]

In particular this includes files needed for running the tests, as well as the changelog.

[codecov]

Codecov Report

Merging #3495 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3495   +/-   ##
=======================================
  Coverage   84.38%   84.38%           
=======================================
  Files         167      167           
  Lines        9376     9376           
  Branches     1392     1392           
=======================================
  Hits         7912     7912           
  Misses       1206     1206           
  Partials      258      258

[kmike]

Thanks @toddrme2178! I think that's fine to add them, I don't see any downsides.

Any particular reason you want them to be included?

[lopuhin]

@toddrme2178 thanks for taking care of this, since we already include tests, makes sense to include all supporting files as well.