[CI] update Ruby/Rails versions matrix (#57)

[CI] update Ruby/Rails versions matrix (#56)

prepare v2.1.0 release

CI tweaks

Use Rails preview interceptors + move CI to GH Actions (#55)

prepare release v2.0.2

Hide delivery form if allow_delivery is false (#54)

prepare v2.0.1 release

:wrench: refactor some specs

Don't show empty mailer classes in sidebar (#51)

ci: ruby-head is not compatible with rails 5.2

update Travis CI badge [ci skip]

docs: highlight Email versions in main Features section [ci skip]

v2 release 🎉 🎉

some refactor and tweaks in css, specs and code style (#50)