Centralized mail handling per post on google + community.

Additions:
classes/trssmailer.php - Created class TTRSS mailer which extends phpmailer and sets the default mail settings upon instantiation. Class includes quickmail function that allows for a quick email send with no extra configuration necessary.

Changes:
config.php-dist - Added the smtp port option

include/digest.php - Converted it to use the new ttrrssmailer class

include/sanity_config.php - Added the smtp port option to the sanity check

plugins/mail/init.php - Modified to use ttrssmailer class. This particular configuration shows a hybrid use case.

register.php = Modified to use ttrssmailer class.

All code was tested and functioned on my local machine.