Change way mails are build

[JDPDO]

Changing the way mails are build.

• [x] Implement recipient behaviour
• [ ] Subdivide put_body-method
• [ ] Templates
  • [ ] Simplify signature insert
  • [ ] to structure e-mails in sections
  • [ ] to insert dynamic data
• [ ] Using AST the whole time to minimize parsing overheads. (Use Swoosh.Email.private map intended for frameworks.)
• [x] Prepare builder for #119: Flag for build function or second public function for live building.

[wmnnd]

I’m closing this for now. If you still want to implement some of those features, please reach out and we can have a chat how to go about that :-)