code: public B getInstance()
              throws BackendInitializationException, BackendNewInstanceException {
          B backend = backendSpec.newBackendInstance();
          backend.initialize(this);
          return backend;
      }
docs: Instantiates a new {@link Backend} and calls its
  {@link Backend#initialize} method before returning it.
  
  @return
  @throws org.protempa.BackendInitializationException
  @throws org.protempa.backend.BackendNewInstanceException