Slowly adding tests

[matthewtownson]

Including more tests on aotools, and bug fixes to tested functions

[codecov-io]

Codecov Report

Merging #20 into master will increase coverage by 4.71%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   69.07%   73.79%   +4.71%     
==========================================
  Files          21       21              
  Lines         996      996              
==========================================
+ Hits          688      735      +47     
+ Misses        308      261      -47

Impacted Files	Coverage Δ
aotools/wfs/wfslib.py	81.39% <ø> (+62.79%)	⬆️
aotools/astronomy/__init__.py	100% <ø> (ø)	⬆️
aotools/turbulence/temporal_ps.py	25% <100%> (+11.11%)	⬆️
aotools/astronomy/_astronomy.py	81.81% <0%> (+54.54%)	⬆️

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