pg_email: Compose and send e-mail messages using template

This class can be used to compose and send e-mail messages defined using template files.

It reads a template file to extract details about the messages to be sent such as the text or HTML contents, the recipient addresses, the subject, etc..

The class processes the template, eventually replacing template variables inserted in the text and HTML body data.

The processed messages can be sent immediately or saved to files. A log file may be updated as the messages are sent.

The class supports validating the e-mail addresses, sending attached files, and protection against header injection.