Implement Step-Over functionality

This change adds a new "Step Over" button, which is enabled
when a "JSR" (Jump to Subroutine) instruction is encountered
while stepping through execution one instruction at a time.

Pressing "Step Over" will continue running instructions until a
corresponding "RTS" (Return from Subroutine) is encountered.
While stepping over a subroutine, the call stack depth is tracked
in an attempt to halt only when the *correct* RTS is encountered.
In other words, it should skip over other subroutines nested
inside the call you want to step over:

```
     JSR A # Step over here...
     ...
     JSR B
     ...
     RTS   # Returns from 'B', doesn't halt
     ...
     RTS   # Returns from 'A', halts after return
```

Implements feature request #18.

README.md

@@ -377,7 +377,7 @@ running.
 
 ## 8.0 Copyright and Acknowledgements
 
-**Copyright (c) 2014 Seth J. Morabito <web@loomcom.com>**
+**Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>**
 
   - Portions Copyright (c) 2014 Maik Merten 
     <maikmerten@googlemail.com>