CI update, badge update, and travis cleanup

[dylan-asmar]

• Updated CI to include ubuntu, windows, and macOS
• Updated README badges
• Added support fo Finite HorizonPOMDPs v0.3
• Added .vscode to .gitignore
• Cleaned up remnants of Travis-CI

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a5e26fd) 96.03% compared to head (484d654) 96.33%.
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #16      +/-   ##
==========================================
+ Coverage   96.03%   96.33%   +0.29%     
==========================================
  Files           2        2              
  Lines         101      109       +8     
==========================================
+ Hits           97      105       +8     
  Misses          4        4              

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