jsx: Support optional props passing

[thangngoc89]

Given the following code:

open Tyxml;
module SearchBar = {
  let createElement = (~query="", ()) => Html.txt(query)
  };
};
let page = (~query=?, ()) => {
    <SearchBar ?query />;
};

This error appears when running through tyxml-jsx :

Error: Unexpected optional jsx attribute query at ?query

rtop -dsource doesn't output anything

cc @Drup