Adding support for nlp-primitives

[ctduffy]

Pull Request Description

Incorporates the nlp-primitives PyPI library into Featuretools.

[codecov]

Codecov Report

Merging #704 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #704   +/-   ##
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  Coverage   97.64%   97.64%           
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  Files         118      118           
  Lines       10173    10173           
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  Hits         9933     9933           
  Misses        240      240

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[kmax12]

@ctduffy can you also add to docs/source/getting_started/install.rst? look at how we do it in #699

[ctduffy]

Add the nlp-primitives API doc to the Featuretools documentation, which will require putting nlp-primitives as a requirement in FT dev reqs