Base type documentation

Adds guides for replacing the default repository type in Symfony 2, Zend Framwork 1 & 2 and Laravel 4.

I've tested the steps required for ZF 1 & 2 and Laravel. For the Zend Framework family, it turns out that a factory implementation was required, so I've gone ahead included a basic version, in a preliminary place; `\Happyr\DoctrineSpecification\RepositoryFactory`. I figure a basic implementation of it is a worthwhile inclusion, to ease integration with other frameworks.
Use `use Happyr\DoctrineSpecification\EntitySpecificationRepository` and then `new EntitySpecificationRepository` instead.