Fix setup.py sdist related issues and use only __version__

[benjaoming]

Seems there were two times MANIFEST and MANIFEST.in

CC: @rsalmaso

[codecov-io]

Codecov Report

Merging #73 into master will decrease coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
- Coverage   75.89%   75.84%   -0.05%     
==========================================
  Files          26       26              
  Lines         560      559       -1     
==========================================
- Hits          425      424       -1     
  Misses        135      135

Impacted Files	Coverage Δ
django_nyt/__init__.py	66.66% <100%> (-4.77%)	⬇️

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