documentation update and re-organization

[heckj]

Provide organization (aka curation) and abstracts for all of the public types in the library.

Motivation:

Updates to the documentation to fill in the missing abstracts for the provided types, updating the language to follow Apple developer content guidelines, and fixing smaller typos and grammar issues.

Modifications:

Curation files added to provide organization for public types, ordering the content to align with the narrative content provided earlier. Updating API comments, adding abstracts and parameters where missing, and moving some of the getting started content that was previously in the main index into a separate article.

Result:

starting point

   --- Experimental coverage output enabled. ---
                | Abstract        | Curated         | Code Listing
Types           | 69% (11/16)     | 38% (6/16)      | 25% (4/16)
Members         | 57% (54/94)     | 3.2% (3/94)     | 0.0% (0/94)
Globals         | 7.1% (1/14)     | 7.1% (1/14)     | 7.1% (1/14)

Updated:

                | Abstract        | Curated         | Code Listing
Types           | 94% (15/16)     | 94% (15/16)     | 38% (6/16)
Members         | 85% (80/94)     | 97% (91/94)     | 0.0% (0/94)
Globals         | 14% (2/14)      | 100% (14/14)    | 7.1% (1/14)

[czechboy0]

Thanks @heckj, a few comments

[czechboy0]

One more set of suggestions, but lgtm otherwise

[FranzBusch]

Overall this LGTM. I left one smaller NIT.