Search and load every installed plugin through entry points.

def load_installed_plugins():
        """Search and load every installed plugin through entry points."""
        providers = {}
        checkers = {}
        for entry_point in pkg_resources.iter_entry_points(group='archan'):
            obj = entry_point.load()
            if issubclass(obj, Provider):
                providers[entry_point.name] = obj
            elif issubclass(obj, Checker):
                checkers[entry_point.name] = obj
        return collections.namedtuple(
            'Plugins', 'providers checkers')(
                providers=providers,
                checkers=checkers)