Find and return a format by content type.

    :param content_type: A string describing the internet media type of the format.

def find_by_content_type(content_type):
    """
    Find and return a format by content type.

    :param content_type: A string describing the internet media type of the format.
    """
    for format in FORMATS:
        if content_type in format.content_types:
            return format

    raise UnknownFormat('No format found with content type "%s"' % content_type)