Add `greatest_raise_at_first_fail` and `-a` option.
Add `greatest_raise_at_first_fail` and `-a` option.

This can be used to raise a SIGABRT on the first failing test. This is
handy in gdb when assertions are non-trivial to breakpoint (in loops,
recursion, callback...) as it'll drop right at the offending assert.

Refactor flags manipulation in option parsing.

Closes #71.

silentbicycle/greatest,silentbicycle/greatest