Fix for issue 109

[rdipippo]

Literals can now be case insensitive, which can be specified with a flag in LiteralArgumentBuilder.

if the flag is true, the literal will be put into the literals hash in CommandNode with its key set to all lower case, and it will be gotten from the hash with a lowercased key.

When CommandNode.parse is called, it will check the flag and do a case insensitive check if necessary.