Allow empty curly brace blocks. Resolves #138

This is literally the easiest change I've ever made to kOS.  It's exactly 1 character of source code changed.  I expected some problems when I tested it - perhaps having branch opcodes trying to jump to nonexistant instructions - but when I tested it seemed to work everywhere from just this one change - if's, else's, until's, when's, on's.  nested complex cases, long if-else ladders with null blocks in the middle, etc.  It seems to work just fine with only changing the syntax config.

(This also causes ParseTree.cs, Parser.cs, and Scanner.cs to be changed, but I left them out of the commit, as they are autogenerated).