Allow passing an array of keys to map each item to an array
.sortBy() now sorts arrays as python does tuples

This allows you to sort by multiple keys -
Adds tests
Merge branch 'better-sort' of github.com:eric-wieser/Sugar into eric-wieser-better-sort

Conflicts:
	lib/array.js
	test/environments/sugar/array.js
moving compareValue out to its own function, also added tests for
mapping multiple values (Issue #386)