Added long form options for all generators (--cpp etc.)

Short-form versions are still supported, but are deprecated.

Change-Id: I15f70ca8d69ba5790368205caa9603b65e1b7fff
Tested: on Linux.

tests/monster_test_generated.js

@@ -352,6 +352,8 @@ MyGame.Example.Stat.endStat = function(builder) {
 };
 
 /**
+ * an example documentation comment: monster object
+ *
  * @constructor
  */
 MyGame.Example.Monster = function() {