Add moment of inertia function

[chrisjonesBSU]

This is useful for rigid body stuff, so I figured we could add it to our "tool box".

I still need to make a unit test for it. Just making the PR now to get another set of eyes on it.

Also, credit to Jenny for writing the function, I just copied it over to this repo.

[codecov]

Codecov Report

Merging #40 (2952c5f) into master (08c1605) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
+ Coverage   99.09%   99.11%   +0.02%     
==========================================
  Files           7        7              
  Lines         331      340       +9     
==========================================
+ Hits          328      337       +9     
  Misses          3        3              

Impacted Files	Coverage Δ
cmeutils/geometry.py	100.00% <100.00%> (ø)

[jennyfothergill]

LGTM :)
Edit: after this is merged, let's bump the version so that any packages that depend on this function (like polyelipsoid) can specify after this version.