UPGRADE

Upgrading from 0.2 to 0.3

Removed the MappedStatement and MappedVerb classes. They are needed for Doctrine based implementations and thus have been moved to the php-xapi/repository-doctrine package. Consequently, the StatementRepository class has been removed too. You now have to implement the StatementRepositoryInterface and handle Statement classes directly instead.
Removed the NotFoundException in favor of the exception with the same name from the php-xapi/exception package.
The public API now uses StatementId instances instead of strings to carry information about statement ids. This means changes to the following methods:
- StatementRepositoryInterface::findStatementById(): The $statementId argument is now type hinted with StatementId.
- StatementRepositoryInterface::findVoidedStatementById(): The $voidedStatementId argument is now type hinted with StatementId.
- StatementRepositoryInterface::storeStatement(): The method returns a StatementId instance instead of a string.
The requirements for php-xapi/model and php-xapi/test-fixtures have been bumped to ^1.0 to make use of their stable releases.

The base namespace of all classes was changed from Xabbuh\XApi\Storage\Api to XApi\Repository\Api.