JS API is not idiomatic or documented

[andreubotella]

It seems like the only way to know how to even use the JS API is to dig into the Rust code. The generated documentation at https://deno.land/x/[email protected]/mod.ts is completely useless.

I think the following changes should be made:

• Make Parser wrap InternalParser, rather than extend it.
• Since all of the methods of (Internal)Parser return promises, make the Parser constructor synchronous and initialize the wasm module on the first method call. We can still keep createInstance for backward compatibility.
• Can we make Parser::parse take a ReadableStream<Uint8Array> and have it acquire a BYOB reader, rather than take the BYOB reader? Or maybe have the JS-side parse method wrapper take a ReadableStream<Uint8Array> | ReadableStreamByobReader.
• Making Parser a wrapper class would take care of having the methods and their argument/return types in the documentation, but there needs to be more documentation on top of that.