Housekeeping

[DannyBen]

A minor Housekeeping PR, including these changes:

1. Add Gemfile, gitignore Gemfile.lock and remove .gems - according to modern common practices for gem development.
2. Remove development requirement from gemspec, and add them to Gemfile instead.
3. Add GitHub Actions test workflow, for Ruby 2.7 and up.
4. Update gemspec with best practices options:
   • Add rubygems_mfa_required
   • Add required_ruby_version - set to the oldest, non-EoL ruby 2.7
5. Prefix makefile tasks with bundle exec so they can properly run in any Ruby setup.

[soveran]

Great job, thank you!