Add force-out support.

[FiV0]

Adding the option to force out of a debugging operation. Also skips
instrumented functions lower in the call stack. Already implemented
at cider-nrepl level.

Replace this placeholder text with a summary of the changes in your PR.
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Thanks!

If you're just starting out to hack on CIDER you might find this section of its
manual extremely useful.

[FiV0]

@bbatsov Are the tests failure due to me or due to me or jorgenschaefer/emacs-buttercup#122?

[bbatsov]

As this is what people see in the menu, I guess we should use different wording here - otherwise it's not clear how it differs from the standard "out".

[bbatsov]

I think we also list the debugger commands in its manual with some extra explanations.

[FiV0]

@bbatsov What do you mean? The big O command is already in the docs.
https://docs.cider.mx/cider/debugging/debugger.html#_keys

[bbatsov]

My bad. I didn't notice this. Thanks!