Implement byte padding for Elliptic Curve point encoding as fix for #173

[webprofusion-chrisc]

Description

This change implements byte padding of Elliptic Curve point byte representations to match the required field size.

Checklist

• [X ] All tests are passing
• [ X] New tests were created to address changes in pr (and tests are passing)
• [X ] Updated README and/or documentation, if necessary

[codecov]

Codecov Report

Merging #174 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #174      +/-   ##
==========================================
+ Coverage   95.21%   95.22%   +<.01%     
==========================================
  Files         103      103              
  Lines        2342     2344       +2     
  Branches      256      256              
==========================================
+ Hits         2230     2232       +2     
  Misses         57       57              
  Partials       55       55

[webprofusion-chrisc]

Ok, I think this is clean enough to leave as-is, unless @fszlin has any suggestions!

[webprofusion-chrisc]

I have added attributes to JsonWebKey and it's derivatives to enforce the serialization order of properties. One user was getting an incorrect Account Key thumbprint during challenges as the key properties were serializing in a different (non-alphabetical) order resulting in a different json string being hashed.