Added num.isNumberType and repurposed num.isNaN

[gphfour]

Adds num.IsNumberType validator which fixes #138
Re-purposes num.isNaN to reflect its actual function.

[codecov-io]

Codecov Report

Merging #139 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #139   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           3      3           
  Lines         410    413    +3     
  Branches       56     56           
=====================================
+ Hits          410    413    +3

Impacted Files	Coverage Δ
packages/toi/index.ts	100% <100%> (ø)	⬆️

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