Update for fw 2.1. See changelog for details. (ouster-lidar#259)

* Add support for the new signal_multiplier config parameter
* Add support for the new 8-bit reflectivity format in simple_viz
* Update Python ouster-sdk package to version 0.2.1, bugfix release
* Remove viz_node and graphics packages from ROS build dependencies
* Ensure ouster_ros dependencies can be satisfied using rosdep
* Various improvements to the ROS img node output

Release 20201209

Release for firmware v1.13.0

Release for firmware v1.12.0

Release for firmware v1.11.0

Release for firmware v1.10.0