docs(CordovaLib): Start filling out DocC comments

[dpogue]

Platforms affected

iOS

Motivation and Context

The API available to people embedding CordovaLib as a framework in their existing apps is not well documented, nor is the API available to plugin authors.

With DocC comments, we can generate Apple-style documentation for our framework, and serve it on GitHub Pages.

Description

Add DocC comments to some of CordovaLib and add a main page file. This is only an initial pass over the sections of code that I've been touching recently, but the goal is to have everything that's public API commented appropriately.

Testing

Existing tests pass.
Built documentation bundle with Xcode for local testing.

Checklist

• I've run the tests to see all new and existing tests pass
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.22%. Comparing base (8e59e52) to head (55e5a33).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1476   +/-   ##
=======================================
  Coverage   80.22%   80.22%           
=======================================
  Files          16       16           
  Lines        1871     1871           
=======================================
  Hits         1501     1501           
  Misses        370      370           

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[erisu]

LGTM

Ran basic tests (Cordova sample app & Cordova Plugins)