Uppercase sheet names don't play well with the Haxe type generation

[Simn]

I don't really care much because I can just use lowercase names, but this threw me off a bit when initially trying to use castledb. Having a sheet name like Enemies messes up the automatic type creation a bit, probably because the name clashes with the type. If this isn't to be supported, it should at least give a sensible error message.