>>> break (> 'c') "abcdabcd" ("abc","dabcd")
break p t == span (not . p) t
fst (break p t) <> snd (break p t) == t
>>> breakEnd (< 'c') "abcdabcd" ("abcdab","cd")
breakEnd p t == spanEnd (not . p) t
fst (breakEnd p t) <> snd (breakEnd p t) == t