Add a helper function to break into the debugger?

[David Peter]

We might consider adding a

dbg::break();

function that would manually set a breakpoint (by raising a signal via __builtin_debugtrap(), __debugbreak(), etc).

See: https://stackoverflow.com/a/49079078/704831

[David Peter]

see also: https://github.com/scottt/debugbreak

[David Peter]

Just reverted the changes from #84.

Let's keep this library focused on "printf debugging". Adding
dbg::breakpoint was actually completely orthogonal to that goal.

Also, there is a much better solution with https://github.com/scottt/debugbreak already.