Asphalt-mailer

- Fixed occasional missing dots in the messages (due to not quoting leading dots)

- **BACKWARD INCOMPATIBLE** Migrated to Asphalt 2.0
- **BACKWARD INCOMPATIBLE** Renamed ``Mailer.defaults`` to ``Mailer.message_defaults``
- Allowed combining ``mailers`` with default parameters
- Fixed default message parameters not being applied in ``Mailer.create_message()``

- Added typeguard checks to fail early if arguments of wrong types are passed to functions

- Initial release