0.5.0 release notes and requirements update

[jcapriot]

release notes for 0.5.0

[codecov]

Codecov Report

Merging #220 into master will increase coverage by 0.89%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
+ Coverage   81.50%   82.39%   +0.89%     
==========================================
  Files          24       24              
  Lines        5233     5499     +266     
==========================================
+ Hits         4265     4531     +266     
  Misses        968      968              

Impacted Files	Coverage Δ
discretize/CurvilinearMesh.py	99.44% <0.00%> (+0.04%)	⬆️
discretize/utils/matutils.py	92.95% <0.00%> (+0.04%)	⬆️
discretize/Tests.py	83.25% <0.00%> (+0.07%)	⬆️
discretize/mixins/vtkModule.py	80.45% <0.00%> (+0.08%)	⬆️
discretize/MeshIO.py	90.42% <0.00%> (+0.11%)	⬆️
discretize/View.py	70.99% <0.00%> (+0.16%)	⬆️
discretize/mixins/omfModule.py	79.74% <0.00%> (+0.52%)	⬆️
discretize/base/base_tensor_mesh.py	91.11% <0.00%> (+0.63%)	⬆️
discretize/TensorMesh.py	81.49% <0.00%> (+0.94%)	⬆️
discretize/CylMesh.py	92.90% <0.00%> (+1.33%)	⬆️
... and 3 more

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