Refactor, encapsulate and test VT escape sequence logic

[Tyriar]

Preferably after #158, the key sequence logic should be largely re-implemented to be better documented, organized, more complete and tested. This effort will fix many issues such as #151, #145, #193, etc.

[Tyriar]

I'm closing this off to keep out issue count lower as it hasn't gained any traction, is stale or is not worth tracking.