Generated parsers no longer export a parser constructor function.
They now export an opaque Language object which can be set on
Documents directly. This way, the logic for constructing parsers
lives entirely in the runtime. The Languages are just structs which
have no load-time dependency on the runtime
My original thought was to decouple the runtime from
the LR parser generator by making TSParser a generic
interface that LR parsers implement.
I think this was more trouble than it was worth.
