Port FW 2.0 and 2.1 changes

[MattSYoung]

Based on my discussion with Steve in #74, there are features in ouster-lidar/ouster_example that have yet to be ported to this repo. I believe (and correct me if I'm wrong) that the last set of changes ported were made with #67. It looks like this PR includes all changes prior to ouster_example/#239.

The goal of this issue is to port across the minimal number of changes to maintain compatibility between the contents of ouster_example/ouster_client and the equivalent files here.

List of features/items to port include:

From ouster_example/#239

• [x] Addition of optional-lite code
• [x] Addition of the sensor_config struct amongst others to types.h
• [x] Addition of new functions to types.h/cpp
• [x] Function changes in lidar_scan.h/cpp
• [x] Addition of new functions to client.h/cpp
• [x] Misc Cmake, readme changes

From ouster_example/#246

• [x] Bugfixes

From ouster_example/#259

• [x] Addition of signal_multiplier parameter to config, across multiple files
• [x] Misc other bug fixes and code changes across ouster_client/ folder

[MattSYoung]

@SteveMacenski Let me know if there is anything here that I've missed.

[MattSYoung]

I think all the changes have been ported, see https://github.com/MattSYoung/ros2_ouster_drivers. I'll do some testing with a physical Ouster and then issue a merge request from that fork.

[MattSYoung]

Confirmed that the changes haven't broken anything (see below). Tested with a OS0-128 at 2048x10 resolution. I will issue a PR now

[MattSYoung]

Closed with the merge of #76