Dezog debugger #35

[rslite]

Implemented serial protocol for communication with DeZog for 48K. Since serial is used, the regular serial logging is turned off by a setting when going through the new Debugger menu entry.

Breakpoints are implemented which allows step into/over, run to cursor.
Pause is implemented in code, but DeZog doesn't send it to zxnext, so for now it's not possible to pause when running unless the code reaches a breakpoints. I have added a new remote type in DeZog, but the code is not good for a pull request yet. An option would be to use the boot button menu and request a pause from there. This wouldn't require a modification for DeZog.
Watchpoints are not implemented and may be difficult to implement but I haven't looked too much into it.

For a debugging session DeZog should be configured to use the zxnext remote type (see below for an example), the Debugger emulator should be started on the Rainbow, and the session can be started with F5.

"configurations": [
{
    ...
    "remoteType": "zxnext",
    "zxnext":{
        "serial": "...",
        "visualMemory": true,
        "memoryModel": "ZX48K",
        "ulaScreen": "spectrum",
        "zxKeyboard": "spectrum",
    }
    ...
}