Release 3.0.0

Added

• Support for PSR-4
• All classes Mailgun\Model are final or abstract.

Changed

• Dropped PHP5 support
• Removed deprecated code
• Moved RequestBuilder and HttpClientConfigurator to Mailgun\HttpClient namespace
• Updated signature of Mailgun::__construct()

Removed

• Dependency on php-http/message.

[Unreleased]

• API v4 Email Validation; please use US Servers with your public key instead
  (please check the Issues 617
  and 619 for further details)