deprecating Swift Mailer and moving all docs into one spot

Author: weaverryan

_build/redirection_map

@@ -417,3 +417,6 @@
 /workflow/state-machines /workflow/introduction
 /workflow/usage /workflow
 /introduction/from_flat_php_to_symfony2 /introduction/from_flat_php_to_symfony
+/email/dev_environment /mailer
+/email/spool /mailer
+/email/testing /mailer