Support for test reporting features needed by other projects

Add XFAIL and SKIP results.
Add a tags: keyword to the protocol: "Tags: (-?(UTF8_NO_WHITESPACE))+" The tags keyword can occur within a test block, and applies only to the test in that case, or outside a test block, where it sets global state for the tags to be applied to all later tests. A tag prefixed with '-' causes that tag to be removed. The python test result objects will gain a "tags" attribute containing a set of the tags applied to the test.