[REQUEST] Enable observation dictionary input.

[Emiyalzn]

Is your feature request related to a problem? Please describe.
Currently, your MDPDataset class assert the observation to be an ndarray object. However, In the field of autonomous driving, the MDP observation cannot be represented by a simple ndarray object. Typically, the observation space can be composed of a BEV image and a speed profile, which is not supported by your MDPDataset yet.

Describe the solution you'd like
I believe it will make the repo stronger to enable observation dictionary storage and training like {"BEV": ndarray(C, W, H), "speed": (1,)} in the MDPDataset (as well as Episode and Transition class).

[takuseno]

@Emiyalzn Thanks for the issue and sorry for the late response. I'm currently pushed by my Ph.D thesis. But, I'm actually working on tuple observation support in nightly branch. Hope this solves your problem once it's released.

[Emiyalzn]

Thank you. I use the rllib to solve my problem, and maybe you can refer to their implementation for some help.

[takuseno]

Good to know you have a working code now. No worry, nightly branch already works now. But, I'm still making more changes until release.