2.0.0-alpha1 - Early release of the upcoming major version!

• Move plain old Email class to Parser\EmailParser — this class is now responsible for parsing emails and creating Email/Fragment objects (see below)
• Move plain old Fragment class to Parser\FragmentDTO — it holds data to build Fragment objects
• Refactor EmailParser code (simplification, more typehints)
• Add (new) Email class that contains a set of Fragment objects, with a read only API => it is a value object
• Add (new) Fragment class — it is a value object
• Refactor tests to fit the new API, however nothing has been broken
• Update README and Composer config
• Extract method to create Email/Fragment objects