modify to support multiple grammars, add fmpxmllayout grammar

The approach taken was to convert the execute() method to route based on grammar and to move all of the parsing into grammar specific parsing methods. Also added an array property to validate that a supported grammar has been specified. fmxmlresult is the default, to support backward compatibility.
Would it be muddying the waters to set the -view command in the useLayoutGrammar method?
RjakesSimpleFm does all of that, but, the whole point of RjakesSimpleFm is that you don't have to understand the URL syntax.