ability to compile to wasm

[lrlna]

To be able to compile to wasm with the current API, we need to wrap the methods we want in JS and format the Error string to JsValue. This adds a bit of overhead, but hopefully in the future we can have something that's more JsError like.

This PR also adds:

• travis check for wasm compilation
• bson-rs package points to my fork until we are all good to merge the outstanding PR in bson-rs
• comments out the integration tests (need to look into using own crate when cargo.toml is set as cdylib.
• adds docs to the readme for the JS-exposed API