Add documentation for creating a resource plug-in

Change-Id: I229316c6f4c634c18fc33b0f5ffd3ce5d194b383
More specific exceptions when validating params

In addition to the example cited in the bug, this updates a few other
exception messages to indicate the name of the parameter that is failing
validation.

Change-Id: I1b7729305988444dc15abd6e5d958f443efc091d
Closes-Bug: #1294295
Merge "Add documentation for creating a resource plug-in"
Merge "More specific exceptions when validating params"