Added support for non-paranthesis based literal argument for message
exchanges in compilation logic.
Changed exitClosureBody to only generate a RET instruction, since the
last expression is implicitly not popped and therefore is ready for a
RET instruction.
Added hooks for enterProgramElements and exitProgramElements to maintain
program element count and index, where null now indicates all
expressions are popped.

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>