Returns the first `Category` member with the matching *value*
        or the specified *default* value if no  member match.

        Example:

        >>> class Format(Category):
        ...     hour = 'hh'
        ...     minute = 'mm'
        ...     second = 'ss'
        >>> Format.get_member('hh')
        Format.hour = 'hh'
        >>> Format.get_member('day', None)

def get_member(cls, value, default=None):
        """ Returns the first `Category` member with the matching *value*
        or the specified *default* value if no  member match.

        Example:

        >>> class Format(Category):
        ...     hour = 'hh'
        ...     minute = 'mm'
        ...     second = 'ss'
        >>> Format.get_member('hh')
        Format.hour = 'hh'
        >>> Format.get_member('day', None)

        """
        for member in cls:
            if member.value == value:
                return member
        return default