fix docs

[knaaptime]

the docs arent rendering correctly
so this pr:

• rebuilds the docs
• add nbsphinx to requirements
• makes area_tables, area_tables_binning, and area_tables_raster private
  • and removes from the api docs

[codecov-commenter]

Codecov Report

Merging #88 into master will not change coverage.
The diff coverage is 93.75%.

@@           Coverage Diff           @@
##           master      #88   +/-   ##
=======================================
  Coverage   81.19%   81.19%           
=======================================
  Files          11       11           
  Lines         569      569           
=======================================
  Hits          462      462           
  Misses        107      107           

Impacted Files	Coverage Δ
.../area_weighted/_vectorized_raster_interpolation.py	63.88% <88.88%> (ø)
tobler/area_weighted/area_interpolate.py	87.28% <88.88%> (ø)
tobler/area_weighted/__init__.py	100.00% <100.00%> (ø)
tobler/dasymetric/masked_area_interpolate.py	90.90% <100.00%> (ø)
tobler/model/__init__.py	100.00% <100.00%> (ø)
tobler/model/glm.py	90.00% <100.00%> (ø)

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