Revert "Revert "Add datafusion-python (#69)" (#257)"

[andygrove]

This reverts commit d0af907 and adds the Python bindings back.

See mailing list thread here

[andygrove]

@alamb @Dandandan @jorgecarleitao

[codecov-commenter]

Codecov Report

Merging #270 (39b1c3a) into master (a9eac57) will decrease coverage by 0.66%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #270      +/-   ##
==========================================
- Coverage   76.87%   76.21%   -0.67%     
==========================================
  Files         133      140       +7     
  Lines       23350    23553     +203     
==========================================
  Hits        17950    17950              
- Misses       5400     5603     +203     

Impacted Files	Coverage Δ
python/src/context.rs	0.00% <0.00%> (ø)
python/src/dataframe.rs	0.00% <0.00%> (ø)
python/src/errors.rs	0.00% <0.00%> (ø)
python/src/expression.rs	0.00% <0.00%> (ø)
python/src/scalar.rs	0.00% <0.00%> (ø)
python/src/types.rs	0.00% <0.00%> (ø)
python/src/udaf.rs	0.00% <0.00%> (ø)
... and 4 more

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[andygrove]

I will go ahead and merge since this was previously approved.