Add necessary output to support realgud mode in Emacs

[Ruin0x11]

Thank you for creating MobDebug. I would like to use it as a part of Emacs, integrated with the realgud package. The problem is the MobDebug server doesn't print a status line when certain events are received, like setting/removing breakpoints. Because of this there is no way for realgud to be aware of these events, so breakpoint indicators can't be shown, as discussed here. This PR adds that output for setb and delb. Also, it adds the ability to pass breakpoint numbers to delb to support breakpoint toggling for realgud, because the command output for the delete command is expected to be similar to that of gdb's, which uses incrementing breakpoint numbers as identifiers instead of file/line.

After adding these changes the debugger integration works pretty well so far with the Emacs plugin I wrote (realgud-mobdebug).