Adding a debugger command

The debugger command will accept anything that would be valid input to the debugger console. This could include informational stuff such as the following:

    po someObject 

It could also include expressions to change the internal state of the program, as follows:

    expr i = 12 

After that expression has been run by the breakpoint, we have a new value of i. No need to stop, change the code, and run again.