Change parser to 3.0

[hmdne]

This is rather an experimental branch to try implementing some Ruby 3.0 features with Opal.

[hmdne]

Wow, oneline methods worked just out-of-the-box

[user@localhost opal]# bundle exec opal -c <<< "def test_oneline_methods = 6" | grep -C4 test_oneline_methods
Failed to load WithCLexer, using pure Ruby lexer
})(Opal);

/* Generated by Opal 1.0.0 */
(function(Opal) {
  var $test_oneline_methods$1, self = Opal.top, $nesting = [], nil = Opal.nil, $$$ = Opal.$$$, $$ = Opal.$$;

  return (Opal.def(self, '$test_oneline_methods', $test_oneline_methods$1 = function $$test_oneline_methods() {
    var self = this;

    return 6
  }, $test_oneline_methods$1.$$arity = 0), nil) && 'test_oneline_methods'
})(Opal);

/* Generated by Opal 1.0.0 */
(function(Opal) {
[user@localhost opal]# 

[elia]

@iliabylich FYI we temporarily disabling c_lexer from the Gemfile, in order to update to parser v3, I'll try to update it later and reintroduce it once it's updated.