Initial commit of changes needed to support XSB debugging in Visual Studio Code
Refactored to make the nested control flow a bit more clear.
Corrected bugs and warnings from my prior debugger.P commits. In particular, properly defined TRACECALLSTACK.
Merge remote-tracking branch 'origin/git-origin' into git-origin
Added g/Goals command to the debugging trace mode. This command prints out the goal stack. Also, changed debugger to exit trace mode and throw an existence error if an undefined predicate is called.