Creates a new font description from a string representation in the form "[FAMILY-LIST] [STYLE-OPTIONS] SIZE", where FAMILY-LIST is a comma separated list of families optionally terminated by a comma, STYLE_OPTIONS is a whitespace separated list of words where each word describes one of style, variant, weight, stretch, or gravity, and SIZE is a decimal number (size in points) or optionally followed by the unit modifier "px" for absolute size. Any one of the options may be absent. If FAMILY-LIST is absent, then the family_name field of the resulting font description will be initialized to NULL. If STYLE-OPTIONS is missing, then all style options will be set to the default values. If SIZE is missing, the size in the resulting font description will be set to 0.