adding more container methods. fixed unary ops.

added container methods for things like getting the size of
a container, or subscripting the container to get/set its contents.

the unary operation opcode execution in the interpreter was busted,
but was fixed by correcting the temporary variable names (x, y, z).
equally important was the incorrect precedence rules in the parser
specification. unary (right-associative) operators needed higher
precedence than the left-associate operators.