Satisfy criteria for REP2004 Quality Level 4

[schornakj]

Master issue for making sure yak_ros2 satisfies the basic minimum requirements for a usable ROS package as defined in REP2004. I wanted to get a head start on this since the Tier 1 platform support requirements for ROS2 are broader than for ROS1.

1. Version Policy

• Implement (and stick to!) semver version policy.

2. Change Control Process
   N/A

3. Documentation

• Make sure licenses are consistent throughout the package.
• Add license blocks to code files.
• Make sure authors are attributed throughout the package.

4. Testing
   N/A

5. Dependencies
   N/A

6. Platform Support
   yak_ros2 is a ROS2 package, so it needs to adhere to REP 2000 and support all Tier 1 platforms:

• For ROS2 Eloquent, support Ubuntu Bionic.
• For ROS2 Foxy, support Ubuntu Focal.
• For ROS2 Rolling, meet same criteria as for Foxy.
• Support MacOS Mojave 10.14
• Support Windows 10 (VS2019)

7. Security
   N/A