Remove PCHIPInterpolation dependency

[bclyons12]

Use PCHIP interpolation available natively through DataInterpolations

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 38.50%. Comparing base (a1519dc) to head (d6a551a).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/math.jl	50.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #48   +/-   ##
=======================================
  Coverage   38.50%   38.50%           
=======================================
  Files          13       13           
  Lines       28439    28437    -2     
=======================================
  Hits        10950    10950           
+ Misses      17489    17487    -2     

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[orso82]

Thank you @bclyons12 !