Automatic evaluation of multidimensional slope expansions

[eeshan9815]

@dpsanders Transferred all the multidim stuff in this PR

[codecov-io]

Codecov Report

Merging #76 into master will increase coverage by 0.85%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
+ Coverage   64.97%   65.83%   +0.85%     
==========================================
  Files          11       11              
  Lines         551      559       +8     
==========================================
+ Hits          358      368      +10     
+ Misses        193      191       -2

Impacted Files	Coverage Δ
src/slopes.jl	82.6% <100%> (+4.03%)	:arrow_up:

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[dpsanders]

Also needs a rebase.

[eeshan9815]

Done