Concatenate operation for Spaces

[ryanjulian]

This is a common use case which leads to a lot of unnecessary munging.

e.g.

    def observation_space(self):
        task_ub, task_lb = self.task_space.bounds
        env_ub, env_lb = super(OneHotMultiTaskEnv,
                               self).observation_space.bounds
        return spaces.Box(
            np.concatenate([task_ub, env_ub]),
            np.concatenate([task_lb, env_lb]))

Could just be

    def observation_space(self):
        task = self.task_space
        obs = super(OneHotMultiTaskEnv,
                               self).observation_space
        return spaces.Box.concatenate(task, obs)

This will require some thought about how non-alike spaces interact, and should provide a feature for concatenating members of these spaces easily and consistent with this spec, once a space is described as a concatenation of other spaces.

Imported from ryanjulian/rllab#2

[ryanjulian]

I'll let @krzentner decide if this is a worthy part of akro.