Add codes and help links to existing warnings

[MattKotsenas]

Before we add more warnings, add warning codes using the format RPBxxxx so that they can be suppressed if necessary.

As part of that work:

1. Renamed Documentation -> docs to better align with conventions
2. Added HelpLinks to error messages
3. Added tests to verify warnings are thrown and can be suppressed with NoWarn

As a follow up we may want to further reorganize documentation, but wanted to keep this change focused where possible.

[baronfel]

Love it - thanks for the docs pages!