More personalisation options and additional email addresses

We have used this plugin quite a bit and had a couple of feature requests to make:

- Ability to add more custom strings to be replaced via the admin interface. e.g. {{custom_string_to_replace}} to be replaced by a user meta field such as display_name

- Ability to specify 'additional' email addresses for members. This is probably more suitable to do in the memberships plugin, but this would be very useful for scenarios where the membership is a 'family' membership and multiple email addresses need to be emailed for one WP user account.

Would be great if these can be added to the roadmap as I'm sure it would be beneficial for a lot of other users/developers.