feat: add support for class, arrows

[pemrouz]

This actually deletes the code that attempts to parse functions in favour of a simpler technique (originally used in utilise/fn) which means all the newer features like classes and arrow functions also work now. Tests added.

[nikbpetrov]

Same applies for constructors in the unwrapConstructor function just above your changes:

function unwrapConstructor(val) {
    if (typeOf(val) === 'string') {
      if (val === UNDEFINED_FLAG) return undefined;
      if (starts(val, FUNCTION_FLAG)) {
        var fn = val.slice(FUNCTION_FLAG.length);
        var argStart = fn.indexOf('(') + 1;
        var argEnd = fn.indexOf(')', argStart);
        var args = fn.slice(argStart, argEnd);
        var bodyStart = fn.indexOf('{') + 1;
        var bodyEnd = fn.lastIndexOf('}') - 1;
        var body = fn.slice(bodyStart, bodyEnd);
        console.log(val)
        return new Function(args, body);
      }
      if (starts(val, DATE_FLAG)) {
        var dateNum = parseInt(val.slice(DATE_FLAG.length), 10);
        return new Date(dateNum);
      }
      if (starts(val, OBJECT_FLAG)) {
        return {};
      }
      if (starts(val, ARRAY_FLAG)) {
        return [];
      }
      if (val === INFINITY_FLAG) return Infinity;
    }
    return val;
  }

becomes this:

function unwrapConstructor(val) {
    if (typeOf(val) === 'string') {
      if (val === UNDEFINED_FLAG) return undefined;
      if (starts(val, FUNCTION_FLAG)) {
        return (new Function("return " + val.slice(FUNCTION_FLAG.length)))();
      }
      if (starts(val, DATE_FLAG)) {
        var dateNum = parseInt(val.slice(DATE_FLAG.length), 10);
        return new Date(dateNum);
      }
      if (starts(val, OBJECT_FLAG)) {
        return {};
      }
      if (starts(val, ARRAY_FLAG)) {
        return [];
      }
      if (val === INFINITY_FLAG) return Infinity;
    }
    return val;
  }

Many thanks for pointing this out - very useful in my case! Wouldn't have figured it out without seeing this PR.