Update the Comparison of Email Notifications Modules Documentation

Problem/Motivation

Currently the Comparison of Email Notifications Modules Documentation is outdated and not in drupal.org's modern documentation system.

Steps to reproduce

Visit the current documentation at https://groups.drupal.org/node/15928

Proposed resolution

Update the documentation and move it to the new Comparison of Email Notification Modules Guide.

Remaining tasks

1. Research current email notification modules
2. Create new documentation pages
3. Update the old documentation to point to the new documentation guide