* added plugins submodule, created two hookspecs, one for adding arguments, one for running code after the argument parsing
* implemented plugins application on main file, changed mechanism for argument parsing
* changed previous parsing function to not create the ArgumentParser, and implemented it as a hook for the parsing mechanism
* added pluggy to required deps
* removed unecessary add_config import
* fixed formatting using black
* restored main link file from master
* moved import of parser to right before the register call, to avoid circular imports
* added tests for the plugins hooks
* removed blank line space
* black reformat
