Rmcreyes/#28 slackevent model

[rmcreyes]

Pull Request

Description

Give a brief description of your changes:
Implemented the SlackEvent class, and created tests for it in tests/model/slackevent_test.py.

Testing

If testing this change requires extra setup, please document it here:

Ticket(s)

Closes #28

(Create a copy of that line for each Github Issue affected,
and replace "Affects" with "Closes" if merging this will close the relevant ticket.)

[codecov]

Codecov Report

Merging #40 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #40   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           3      4    +1     
  Lines         105    145   +40     
=====================================
+ Hits          105    145   +40

Impacted Files	Coverage Δ
tests/model/slackevent_test.py	100% <100%> (ø)

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