Gym environment for Carla

How to use

Install the Carla library into Python.

CD to Carla/PythonClient folder, then type:
```
pip install -e .
```
install the package, CD to gym-carla folder, then either:

to copy & install
```
pip install .
```
to be able to edit the code and install:
```
pip install -e . 
```
Carla_0.8.4 fix the collision counting problem and is requred here.
To use, import the gym_carla package in the code, together with gym.
```
import gym
```
```
import gym_carla
```
```
client = gym.make('Carla-v0')
```
then it can be used by calling functions of seed, reset, step, close, render
To launch Carla, add CarlaUE4 to PATH, then use the script launch_carla.bat or launch_carla.sh to launch Carla.