* Fixes incorrect loop `next`ing behaviour
* Includes fix for determining return address

Improvements:
* `next`ing through a loop works correctly (when not already within a loop)
* `next`ing out of a function works correctly

Needs work:
* `next`ing in a loop can be improved when starting within a loop

This current implementation does not cover the following:

* Setting correct breakpoint when exiting loop
* Setting correct breakpoint when returning from function
    * All facilities are available for this, it just is not taken into
      account in the current `next` implementation.

Benefits of this CL:

* Commands no longer rely on closured proc struct
* No two-step process for basic command initializaion

Implement basic api for figuring out, given a current PC value, where
the function will return. Currently the API provides only a way to
determine the offset from SP (the Canonical Frame Address). It is left
up to the caller to grab the actual address from the traced program.

Also change function sig to be shorter

Still needs to handle the following:
* Correctly adapt to augmentation strings
* Correctly parse instructions