Support pause and continue requests

[ddoktorski]

Closes #5
Closes #6
Towards #3

[ddoktorski]

This change is part of the following stack:

• Remove main.rs #25
  • Add client connection handling via I/O threads #27
    • Move debugger to separate module #28
      • Make handle_request method of debugger #29
        • Add initialization flow #30
          • Integrate debugger with VM #31
            • Support pause and continue requests #32 ◀
              • Add debugger state #38
                • Separate request handling and client communication #39

_{Change managed by git-spice.}