passed explicitly to each method call. Because of the way the caching
system works, specifying a default size on the constructor doesn't imply a
performance gain over manually passing the size on each function call.
+ If the font is bitmap and no *size* is given, the default size is set
+ to the first available size for the font, if possible.
If the font file has more than one font, the font to load can be chosen with
the *index* argument. An exception is raised for an out-of-range font index