Build the .napp file to be sent to the napps server.

        Args:
            napp_identifier (str): Identifier formatted as
                <username>/<napp_name>

        Return:
            file_payload (binary): The binary representation of the napp
                package that will be POSTed to the napp server.

def build_napp_package(napp_name):
        """Build the .napp file to be sent to the napps server.

        Args:
            napp_identifier (str): Identifier formatted as
                <username>/<napp_name>

        Return:
            file_payload (binary): The binary representation of the napp
                package that will be POSTed to the napp server.

        """
        ignored_extensions = ['.swp', '.pyc', '.napp']
        ignored_dirs = ['__pycache__', '.git', '.tox']
        files = os.listdir()
        for filename in files:
            if os.path.isfile(filename) and '.' in filename and \
                    filename.rsplit('.', 1)[1] in ignored_extensions:
                files.remove(filename)
            elif os.path.isdir(filename) and filename in ignored_dirs:
                files.remove(filename)

        # Create the '.napp' package
        napp_file = tarfile.open(napp_name + '.napp', 'x:xz')
        for local_f in files:
            napp_file.add(local_f)
        napp_file.close()

        # Get the binary payload of the package
        file_payload = open(napp_name + '.napp', 'rb')

        # remove the created package from the filesystem
        os.remove(napp_name + '.napp')

        return file_payload