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/generate_code.sh

@@ -1,2 +1,2 @@
-../flatc -c -j -n -g -b -p -s --php --gen-mutable --no-includes monster_test.fbs monsterdata_test.json
-../flatc -b --schema monster_test.fbs
+../flatc --cpp --java --csharp --go --binary --python --js --php --gen-mutable --no-includes monster_test.fbs monsterdata_test.json
+../flatc --binary --schema monster_test.fbs

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() {