Refactor wasm library so it can be used as a backend for a JS frontend

[io12]

No description provided.

[aweinstock314]

Adding top-level functions decorated with #[wasm_bindgen] to the js_interop module will make them available to JS that loads the wasm blob.

I'm not sure what all the features Connor wants are, but parsing a JsString into an Expr (possibly serializing it to JSON instead of returning a pointer to the WASM heap), enumerating rules (e.g. exposing RuleM::ALL_SERIALIZED_NAMES as a JS Array of JS Strings), and checking a (subproofless) rule given a vector of deps seems like a starting point.