Update use of modularized grammars

[thec0keman]

PegJS is working on support for modularized grammars. Once this is finalized and released, it would be good to update emblem to take advantage of this (over against use of pegjs-import).

There are a couple of issues with our current structure:

1. modules are copied when imported, so emblem's size grows as you reuse a module
2. circular dependencies do not work, which has resulted in some less than intuitive module structure. (In general, it forces pushing shared code higher in the chain).

Tracking issue.