Allow memcache to connect to a host/port

Allow loading of an external container (#19)

* Allow loading of an external container

* Update README.md

Make all constructors public

Now they can be used with an external dependency injection framework

Bugfix for ORM: Invalidate cache after insertion when memache disabled

Return a value from prefetch if result is false

Remove PHP 7.0 from build

Fix tests, improve coverage

Fix tests

Merge branch 'master' into allow_json_mapping

Lower php verison requirement