Document empty array()->end == -1

[skip ci]
	modified:   lib/List/Objects/WithUtils/Role/Array.pm
	modified:   t/01_array/end.t
minor test tweaks

	modified:   t/01_array/diff.t
	modified:   t/01_array/join.t
	modified:   t/01_array/kv.t
	modified:   t/01_array/pop.t
	modified:   t/01_array/random.t
	modified:   t/01_array/shift.t
	modified:   t/01_array/sliced.t