Add tests for creating arrays with %w
Remove examples for creating arrays with %w
Add test for use of 'next' keyword
Remove example of use of 'next'
Add tests for use of .at; create/make use of shared example for out-of-range indexes
Add test for .assoc not returning existing non-array elements
Add tests for .rassoc
Rework shared examples, tests for .assoc/.rassoc
Add tests for .assoc/.rassoc returning the first of numerous appropriate arrays
Touchup spacing, reword notes, replace test expectations