Add array->lastidx

Also add aliases to help my brain:
  first_index -> firstidx
  last_index  -> lastidx

Still undecided on array->last.
Too confusing vs array->end.

May go:

  first -> first_where
   (keep ->first for backwards compat)
  add last_where

	modified:   lib/List/Objects/WithUtils/Role/Array.pm
	modified:   t/01_array/firstidx.t
	new file:   t/01_array/lastidx.t
Typo fix

	modified:   t/01_array/firstidx.t