Update the description of the CDM specification

[shivmgg]

Following changes are added to the CDM specification:

• The changes ensure that the current module implementation is core-independent.
• Adds a much better and illustrative image for the high-level overview of run-control debugging.
• The register map is updated.
• The description of debug stall packet and index files are updated.

Closes #11

[imphil]

Thanks for the update @shivmgg. I've looked through it, looks mostly good to me! I noted a couple things and instead of iterating on this for very long I went ahead and made the changes before rebaseing and merging this PR.

On a technical note: you can update a PR in any way by using git's history rewriting functionality (e.g. git rebase -i or git commit --amend) and force pushing (git push -f) to the branch that represents this PR.

Let's now move the discussion back to the mailing list and see what the next steps are.