clean generated project files

def clean(ctx):
    """
    clean generated project files
    """
    os.chdir(PROJECT_DIR)
    patterns = ['.cache',
                '.coverage',
                '.eggs',
                'build',
                'dist']
    ctx.run('rm -vrf {0}'.format(' '.join(patterns)))
    ctx.run('''find . \( -name '*,cover' -o -name '__pycache__' -o -name '*.py[co]' -o -name '_work' \) '''
            '''-exec rm -vrf '{}' \; || true''')