Update package doc strings with working URLs

[evanofslack]

All of the reference URLs in the comments currently point to web pages that no longer exist. This pull request is focused on updating these URLs to point to current API reference pages. Currently only the rest package docs have been updated.

Additionally, this request does some minor housekeeping including:

1. Update some method comments to better reflect the wording on API reference pages.
2. Rearrange some methods for more logical grouping.
3. Refactor CreateUserResponse struct for readability.

[evanofslack]

Looks like the developer docs just changed a bunch of URLs. Previously most of the endpoints were grouped under "team collaboration" and have been updated to a new group called "core". This changes a lot of the URLs added in this PR. Although the previous URLs seem to redirect correctly most of the time, I might as well go back through and add the most recent URLs.

[evanofslack]

Ok all REST endpoint URLs should now match developer docs @geekgonecrazy

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