Copy doc comments from Rust to JS

[fitzgen]

Would be good for JS programmers reading the generated JS to have documentation on

• Classes
• Methods
• Functions
• Anything else that gets emitted and has a doc comment in the Rust version

[FreeMasen]

Would that require a modification to #23 to include the doc comment strings?

[alexcrichton]

Indeed! That's fine though, the format isn't specified yet :)

[FreeMasen]

After #265 we are now copying doc comments from Rust to JS for the following using the JSDoc format.

• Classes
• Methods
• Public Attributes
• Functions

The only other doc comments that I can think of would be module level comments.

One of the nice things about the JSDoc comments is that they define the tooltip content when working in VSCode. I would ideally like to see the following annotated lines added to our current translation.

• @constructor: When using no-modules this would be added to the prototype function
• @param {type} name: This would be added for each parameter in a function signature
• @returns {type}: This would be added to functions and methods that return non-unit types
  • We could also have unit returns annotated with void

Both @param and @returns optionally can have a description added to them, I do not believe that Rust Doc comments have this feature?