Adding predefined parsers.

I still need to find a way to make them at the module level. Probably with static this { ... }
Putting the hooks outside the named!() expression, to allow dynamically added rules to have their own names.
Playing around with rules-adding.

That seems to work, more or less: Pegged can create a static grammar with hooks.
Then dynamic rules can be added, using the functions from pegged/dynamicpeg.g
And now these rule can refer to static rules also. Thus a grammar can be extended from outside.