Add markymark pod and support markdown in UILabel

[kindraywind]

What's in this PR:

• Added markdown support for summaryLabel, descLabel in SummaryTableViewCell and EventTableViewCell
• Added NSAttributedString extension for parsing markdown -> AttributedString

[codecov[bot]]

Codecov Report

Merging #10 into master will increase coverage by 1.79%. The diff coverage is 94.28%.

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
+ Coverage      59%   60.79%   +1.79%     
==========================================
  Files          18       20       +2     
  Lines         700      727      +27     
  Branches       34       32       -2     
==========================================
+ Hits          413      442      +29     
  Misses        284      284              
+ Partials        3        1       -2

Impacted Files	Coverage Δ
...ntsCalendar/Views/Cells/SummaryTableViewCell.swift	0% <0%> (ø)	:arrow_up:
...sCalendar/Utils/NSAttributedStringExtensions.swift	100% <100%> (ø)
...ventsCalendar/Views/Cells/EventTableViewCell.swift	95.12% <100%> (ø)	:arrow_up:
...sCalendarUITests/EventTabViewControllerTests.swift	100% <100%> (+4.87%)	:arrow_up:
...endarTests/NSAttributedStringExtensionsTests.swift	100% <100%> (ø)
...CalendarUITests/EventFeedViewControllerTests.swift	100% <100%> (ø)	:arrow_up:

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