Number - ++ ans -- now work.
Grammar1 - UnaryOperationNode was added (replacing MonadicOperatorNode).
Executor - comment was slightly modified.
SnowORHail.g - expression grammar was renewed based on Groovy grammar.

Now the grammar supports nested function/method call as well as for/if statements.
This grammar still generates NullNode entries for empty lines, and therefore,
Parser.cc should take care (i.e. erase) NullNodes to speed up execution.