Find and return a format by name, acronym or extension.

    :param identifier: A string describing the format.

def find(identifier):
    """
    Find and return a format by name, acronym or extension.

    :param identifier: A string describing the format.
    """
    for format in FORMATS:
        if identifier in [format.name, format.acronym, format.extension]:
            return format

    raise UnknownFormat('No format found with name, acronym or extension "%s"' % identifier)