Remove all ++ and -- operators

[marcusnaslund]

++variable is semantically +(+(variable)) and generates the C code ++variable because of no special-casing. On the other hand, variable++ simply doesn't parse.

The fact that ++variable actually works is a mistake/bug in rock and will be fixed soon - see ooc-lang/rock#982

Therefore, we should avoid it all-together. It is confusing in itself that ++variable works but variable++ does not.