Address improper use of recipients field - fixes spree-contrib/spree_email_to_friend#56
Remove html from flash message

Fixes spree-contrib/spree_email_to_friend#55
Test 2.1.5
Update README.md etc.

- Move contributing information to own document.
- Fixes badges.
Semantic versioning.
Correct dev/test version for 2-2-stable branch.
Update dev dependencies.
Fixes RSpec deprecation warnings.
Remove .html_safe from controller.