First steps toward an MessageBuilder class
Removed validation from Builder that's done on construction
Removed length validation on sending

and added it on construction
Moved private setters down and added PHP doc to them
Added isValidated to certificate
Added toString and Serialization to the Message
Intro in Upgrade.md
Fixed a serie of tests
Certificate class is now also Serializable
Merge branch 'refs/heads/development' into feature/message-builder
Merge branch 'refs/heads/development' into feature/message-builder
Docfix + removed unused variable
Fixed testsuite, all tests pass again
Merge branch 'refs/heads/feature/message-builder' into development