Improved script usage
Improved script usage

Added options `--clean` & `--help`
If the script is ran without options, it builds & installs the source and generate docs.
When `--clean` is used, it will perform clean build by deleting install folder.
When the script is ran with invalid/accidental args, help message is shown.
dronecore/DroneCore,dronecore/DroneCore,dronecore/DroneCore,dronecore/DroneCore