Call Instruction

[alexdovzhanyn]

Adds functionality for the :call instruction. Also slightly changes the way WaspVM executes the initial function call.

When a :call instruction is encountered, WaspVM:

• Finds the address of the function that is being called
• Fetches the function from the store
• Creates a new frame with the function call, passing in the current VM state
• Once the function call completes, it returns the VM so that the program may continue

We're currently using a single stack for all functions -- but it may be beneficial in the future to allow each function to have its own stack