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.
ok, but the grammar property is stored as lower case. I leave it to the URI property to get the case of the URI correct, so, the test for FMPXMLLAYOUT is pointless and confusing. They should both user strtolower.