ENH: Shorten tracebacks, e.g. with `__tracebackhide__`.

[tobiasraabe]

Is your feature request related to a problem?

For example, if you quit the debugger, a long stack trace is printed including the position where the exception to quit the debugger is raised.

Describe the solution you'd like

This could be hidden from the user by filtering stack frames for variables like __tracebackhide__ = True.

API breaking implications

None.

Describe alternatives you've considered

Not yet.

[tobiasraabe]

Closed in #129.