Addition of CartPole Environment, and some Error Corrections

[hojin1117]

Hi Taekyung Kim,
the objective of this request is to add continuous cartpole environment and to apply slight modifications on your work.

1. New Environment

• I added continuous action cartpole environment in your work. Unlike cartpole environment of openAI gym in which action is discrete(Left or Right), in this environment, action varies continuously from -10.0 to 10.0.
• The magnitude of wind is converted into magnitude of torque(wind_torque), and then it is applied to system dynamics in 'step' function.

2. Error Correction

• If the sign of wind is plus(+), wind blows from left to right. Otherwise, wind blows from right to left. So I modified 'Line 117-118' of 'unstable_pendulum.py' to fit this sign convention.
• Deletion of some print commands in 'unstable_pendulum.py'
• Some Typo Corrections

Thanks for your great work, Taekyung.

[tkkim-robot]

Thanks for your work hojin1117.

I reviewed your commits and I think it is suitable to merge to master.

But I'm afraid the visualization in "unstable_pendulum.py" is still correct on the original version.
Please check the 'sign' again and let me know.

Best.

[hojin1117]

Hi Taekyung Kim,
I modified sign convention on "unstable_pendulum.py", and renamed some files for simplicity.
Thanks for your great work.