Add Arm and Event API

[patking02]

Fixes #276 and #277

Adds Arm and Event API methods, tests, and documentation.

I initially was going to separate these two out (one PR for Arm, one for Event), but while writing the tests for Arm, I realized I needed to attach an Event to the Arm in order for the Arm Export to return the newly added arm. If need be, I can do one at a time (I guess Event then Arm), but if it is OK to submit/review both at the same time, then here they are.

I tested the Unit tests, but I did not have access to run the Integration Tests, FYI.

[pwildenhain]

Amazing thank you! I'll take a look at some point this weekend or early next week

[codecov[bot]]

Codecov Report

Merging #278 (46bbf78) into master (a168006) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #278   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           19        21    +2     
  Lines          571       625   +54     
=========================================
+ Hits           571       625   +54     

Files	Coverage Δ
redcap/methods/__init__.py	100.00% <100.00%> (ø)
redcap/methods/arms.py	100.00% <100.00%> (ø)
redcap/methods/base.py	100.00% <ø> (ø)
redcap/methods/events.py	100.00% <100.00%> (ø)
redcap/methods/user_roles.py	100.00% <ø> (ø)
redcap/methods/users.py	100.00% <ø> (ø)
redcap/project.py	100.00% <ø> (ø)

[patking02]

Thanks for the kind words; the PyCap library is well maintained and has a lot of good checks and standards in place that made my job easy.

Happy to help contribute and give back to the community. Thank you for reviewing the PR.