Introduce parameterized Rust / Rust Comment writers.

[MaulingMonkey]

Currently, a maliciously crafted .jar can probably inject naughty code into the generated bindings. A proper parameterized API for writing code would do a lot to tighten up this security gap.

Of course, if you're using a maliciously crafted .jar, you're probably already pretty screwed on the security front - but if you're only running the outputs in a nicely constrained sandbox or other security context, I'd like to avoid contributing to any means of badware escaping said sandbox or security context.

[MaulingMonkey]

This could use the #[doc] attribute, especially in the context of macro codegen.