Analytics - Look into Ahoy_email

[ACPK]

The README mentions that a number of analytics features still need to be added. What about recommending that users use ahoy_email if they'd like analytics? @ankane is an amazing developer and I highly recommend a number of his gems including Mailkick, Ahoy, Ahoy_Email, and blazer.

If users would like to see the stats within maily_herald's dashboard, the steps would be:

1. Add a line to the README that users need to integrate ahoy_email for analytics.
2. I can make a PR so maily_herald checks to see if the user is using ahoy_email. If the user is, then maily_herald's dashboard could pull the email analytics from the site' database. These analytics would be saved by ahoy_email.