resolves #735 remove all string mutation operations
resolves #731 add initial Cucumber test infrastructure

- add cucumber and rspec-expectations dependencies
- add cucumber Rake task definition
- add sample cucumber tests and a step definition rough-in
- set version ranges for library dependencies
Merge pull request #733 from mojavelinux/issue-731

resolves #731 add Cucumber test infrastructure
Merge pull request #736 from mojavelinux/issue-735

resolves #735 remove all string mutation operations
resolves #676 substitute anchor and xref macros in footnotes