Add Y.ArraySort.naturalCompare().

For performing natural-order comparisons of two strings, two numbers, or a
number and a string.
Fix comment typo.
Fix lint errors in ArraySort tests.
Fix missing types in naturalCompare() API docs.
'foo10' would be sorted before 'foo2', not 'foo1'.
Merge branch 'dev-3.x' into natural-sort
Build arraysort.
Add missing unit tests.