* develop: (47 commits)
  Migrated Travis CI from .org domain to .com
  Add shell script to push test coverage results to CodeClimate
  Add linters and commit hooks to validate code prior to commits
  Fix bug in Travis CI config
  Bump version to `2.1.0`
  Update Travis CI config to build with latest dependencies and no development gems
  Move gem development dependencies into the `Gemfile`
  Add `:mode` config option; values `:loose`, `:moderate`, `:strict`; default to `:loose`
  Update config for Travis CI
  [readme] Update TravisCI badge URL
  [readme] Add alternate gem `email_verifier`
  [readme] Add alternate gem `email_address`
  Update `CHANGELOG`; bump version to `1.9.0.pre`
  Add `require_fqdn` option, require FQDN by default
  Add support for IPv4 and IPv6 address hosts
  Add Rubocop, `.editorconfig`; code cleanup/linting
  RSpec: Configure zero-monkey-patching mode
  whitespace
  Regex tweak
  [readme] Update `README` to show installating from `karlwilbur` GitHub repo.
  ...