Support anonymous and arrow callbacks

[ivov]

This PR enables evaluation for anonymous and arrow callbacks, which currently fail with Expression is not valid: missing ) after argument list and Expression is not valid: Malformed arrow function parameter list, respectively.

Supported:

• same-line anonymous callback
• single-line anonymous callback
• multi-line anonymous callback
• same-line arrow callback, no body
• same-line arrow callback, with body
• single-line arrow callback

const tmpl = require('./dist/tmpl.js').tmpl;

const anon1 = tmpl('{ [1, 2, 3].filter(function (v) { return v > 2 }) }');
const anon2 = tmpl(`{ [1, 2, 3].filter(function (v) {
  return v > 2
})}`);
const anon3 = tmpl(`{ [1, 2, 3].filter(function (v) {
  const a = 1;
  return v > 2
})}`);

const arrow1 = tmpl('{ [1, 2, 3].filter((v) => v > 2) }');
const arrow2 = tmpl('{ [1, 2, 3].filter((v) => { return v > 2 }) }');
const arrow3 = tmpl(`{ [1, 2, 3].filter((v) => {
  return v > 2
}) }`);

console.log(anon1);  // [3]
console.log(anon2);  // [3]
console.log(anon3);  // [3]
console.log(arrow1); // [3]
console.log(arrow2); // [3]
console.log(arrow3); // [3]

[GianlucaGuarini]

Thank you for your PR, riot-tmpl is no longer maintained and it was meant to be used on ie9 (during the pre template literals javascript era).
Your PR uses Regex named groups that are not supported on IE so we can not merge it.

Notice that nor arrow functions are supported on older browsers so adding this feature to this package is unnecessary.

Please use template strings on modern browsers and this package on old legacy ones.

Thank you anyway