By default all services created through the `get` method were shared,
first call creates an instance, and every another call return the
previously created instance.
Providing service name in "shared" allows to disable this functionality
for a specific service. Then every call of the `get` method creates
brand new instance of the service.
It is possoble to disable shared services by default for all services
by using `shared_by_default` option to boolean `false`.

Allows removing repository, pinning to a (semi-) stable version, and
using the shipped abstract class.