export parser only

Hi Evan,

I checked [the demo](http://evanw.github.io/glslx/) and it looks very impressive! I'm not familiar with`Skew`, I'm just curious if it would be possible to add a make target which would export only parser part of the library?

Start by reviewing the repository's build setup and the parser entry point, then compare them with the linked demo and the Skew-based library output. Determine whether a parser-only export is supported by the current structure and define completion as a make target that produces only that parser component.

Written by the indexing model from the issue text.