Macros for cleaner export Nim code

[jfilby]

It would be great to use macros to simplify the syntax of repetitive code.

E.g. instead of module.registerFn(3, "testWithArgs"): you could write registerFn testWithArgs (3 args):.

There are other possibilities too. Just an idea, not high priority.

[georgelemon]

Or, even better, using a pragma, something like {.export_napi.}. Should simplify many things:

• Can collect param names/types
• Can check for types and throw NAPI error on type mismatch
• Can create a beautiful JS-like block comment to print description, args and types (when throwing error), something like

  /**
  * Something useful here
  * @param {string} name
  * @param {int} age
  * @param {object} address
  * @param {number} zipcode
  * @return {string}
  */
  Error: Type mismatch parameter: `name`. Got `undefined`, expected `string`

Registering a new function using {.export_napi.}:

init proc(module: Module) =
  proc testWithArgs(name: string, age: int, address: object, zipcode: int = 123) {.export_napi.} =
    ## Something useful here
    echo args[0].getStr   # output `name`
    echo args.get("name") # output `name`
    return %* "Alright!"

[jfilby]

Sounds good.