brightness: Refactoring command line code
brightness: Refactoring command line code

Changes include:
    * Better handling of the command line arguments.
    * Thorough error handling.
    * Stricter type (float / double) use.

stefonarch/lxqt-config,lxde/lxqt-config,lxde/lxqt-config,lxde/lxqt-config,stefonarch/lxqt-config,lxde/lxqt-config,stefonarch/lxqt-config