Accept return value from nested function

[CodyFagley]

Nested functions are being called correctly, the return value is not handled at all.

• If a nested function's return register is not active in the parent function:
  • Parent function should push the return register directly into it's register stack
• If a nested function's return register is active in the parent function:
  • Parent function should push the return register into a new register before restoring active register's value