Add smtp.starttls config.

See https://github.com/fuel/email/issues/55
Merge pull request #639 from kenjis/update_email

Add smtp.starttls config, and some fixes
Merge branch '1.8/develop' into upstream-1.8-merge

Conflicts:
	packages/email/introduction.html
Merge pull request #552 from kenjis/upstream-1.8-merge

本家 1.8/develop をマージ