Create databases for each engine and return a new :class:`.Mapper`.

def database_create(self, database, **params):
        """Create databases for each engine and return a new :class:`.Mapper`.
        """
        binds = {}
        dbname = database
        for key, engine in self.keys_engines():
            if hasattr(database, '__call__'):
                dbname = database(engine)
            assert dbname, "Cannot create a database, no db name given"
            key = key if key else 'default'
            binds[key] = self._database_create(engine, dbname)
        return self.copy(binds)