Previously the generated parser had an intermediate local variable
`result` that really useful if you're building up a stateful object but
Journey always discards the result argument to the reduce functions.
This produces a simpler parser for anybody who actually wants to read
the thing.
Sadly, there's no real performance speedup with this change.
Move the Journey code underneath the ActionDispatch namespace so
that we don't pollute the global namespace with names that may
be used for models.
Fixesrails/journey#49.
