feat(static): support `Path` arg in `App.add_static_route()`

[vgerak]

Summary of Changes

Minor py3.5 compatibility change, to allow pathlib.Path argument types to be provided in App.add_static_route()

Related Issues

Closes #1962

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[codecov[bot]]

Codecov Report

Merging #1970 (d48cd9a) into master (9152c53) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1970   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           63        63           
  Lines         6621      6624    +3     
  Branches      1067      1068    +1     
=========================================
+ Hits          6621      6624    +3     

Impacted Files	Coverage Δ
falcon/app.py	100.00% <ø> (ø)
falcon/routing/static.py	100.00% <100.00%> (ø)

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[CaselIT]

Well it's not a hot path so we could just do an isinstance(directory, Path) and convert to string there (also maybe adding a todo: remove once we drop py3.5

[CaselIT]

thanks for the update!