Find all files in a subdirectory and return paths relative to dir

    This is similar to (and uses) setuptools.findall
    However, the paths returned are in the form needed for package_data

def subdir_findall(dir, subdir):
    """
    Find all files in a subdirectory and return paths relative to dir

    This is similar to (and uses) setuptools.findall
    However, the paths returned are in the form needed for package_data
    """
    strip_n = len(dir.split('/'))
    path = '/'.join((dir, subdir))
    return ['/'.join(s.split('/')[strip_n:]) for s in setuptools.findall(path)]