Cleaned up RSpec 2.14 -> 2.99 deprecation warnings.

This was done by adding the `rspec-collection_matchers` Gem to allow us
to continue using expressions like `expect(foo).to have(5).bars`. Also
made several changes in the style of `describe :foo.to_s` rather than
the previous `describe :foo`, as 2.99 generated a deprecation warning
EVEN THOUGH we were using it correctly for RSpec 3. Pfffft.

RSpec: 86 examples, 0 failures
Script: 0 tests: 0 failures, 0 errors, 0 pending, 0 omitted
RuboCop: 27 files inspected, no offenses detected
RuboCop global overrides in `.rubocop.yml`: 2
RuboCop local overrides in our source/spec files: 5