4.0.0: Upgrade package to PHP 8.3

Drop all support for PHP < 8.3 and add missing type hints.

3.0.0: Re-designed Mail package to be much simpeler.

Re-designed Mail interface (renamed to Mailer) to send a simple data object instead of doing all the logic in the mailer implementing this interface. This is because the methods (now in the data object) never changes but different methods of sending the email have been made. So setting it up this way we need to implement only 1 very simple method and can do only the sending logic in the class implementing this interface.

2.0.1: Removed getters from interface.

Removed getters from interface because they are never being used, we just set the data and send the mail.

2.0.0: Total redesign (simplifying) of mail interface.

Because this interface is being used a lot we found some flaws/short-comings in how it was designed.

For example:
* We always use it to send html mails and never plain text mails.
* The exceptions are never used/thrown because in the implementing classes we mostly rely on php's build-in exceptions like RuntimeException.
* It's damn annoying to write implementations for the MailAddress MailSubject etc classes because they are always the same, also in the general sense of things a string will do which can be validated in implementation if needed. The same rule applies on the Attachment class, so we added it here.

1.0.0

Reformat/rearrange code and added missing docblocks.