Add python package with class FollowMe

This class is a python interface to the `follow_planner`.

Example usage:

```python
import rospy
import geometry_msgs.msg as GM
from follow_planner import FollowMe

sub = rospy.Subscriber("pipol_pose", GM.PoseStamped, callback)
fm = FollowMe()

def callback(data):
    fm.update(data)

fm.start()

# ...
fm.stop()
```