Add Python 3 support

[lights0123]

Closes #13

Should be compatible with existing Python 2 installations and new Noetic builds

[gmsanchez]

Hi! This commit helped to make the reach_ros_node work with ROS Noetic, however the latitude and longitude values are not correct if you live in the south-west hemisphere. I think this code address that issue (worked for me), but I don't know about Python3 and Python2 compatibility.

        latitude = data['latitude']
        if data['latitude_direction'] == str(b'S'):
            latitude = -latitude
        self.msg_fix.latitude = latitude
        longitude = data['longitude']
        if data['longitude_direction'] == str(b'W'):
            longitude = -longitude```