Alternative Update to ROS 1 Melodic

[mabelzhang]

This is an alternative to #4 to update to ROS 1 Melodic. We made quite a bit of changes, but we believe these changes make the package cleaner and update it to standard practice in ROS 1.

Changes we made:

• ROS-packagify drivers/C into hri_c_driver, to eliminate the duplicate C files that exist in both drivers/C and hri_safety_sense directories. We tested that the C tutorials still compile and run using the pure Makefile, if the user does not wish to use ROS.
• Move header files in drivers/C into include/<package_name> subdirectory, which is standard ROS practice
• Clean up README files
• Fix warning about comparing unsigned int with -1
• Remove unnecessary files.