API Remove Director::$test_servers / $dev_servers
API Remove MODULES_PATH / MODULES_DIR constants
ENHANCEMENT Injector backtick syntax now supports environment variables as well as constants
Fixes#6588
API Add HasRequestHandler interface
API Refactor Link() and url handling behaviour from Controller into RequestHandler
API RequestHandler classes now must define url_segment to have a default Link()
API Clean up redirectBack()
* API Replace existing Email and Mailer classes with SwiftMailer powered email system
* DOCS New Email docs
* Initial feedback from Damian
* Making Mailer an interface
* Templates relocated
* Round of feedback
* More robust approach to plain parts
* Revert changes to TestMailer
