Manual: added warnings about some common escaping mistakes.
Manual: added warnings about some common escaping mistakes.

pradeepmurugesan/incubator-freemarker,apache/incubator-freemarker,woonsan/incubator-freemarker,awils18/incubator-freemarker,awils18/incubator-freemarker,woonsan/incubator-freemarker,pradeepmurugesan/incubator-freemarker,apache/incubator-freemarker