Optimized text operators

• The xyshow operator provides a more natural way for applications to deal with individual character positioning. Allows simultaneous track kerning, pair kerning, and justification. Benefits: Performance, convenience.
• The selectfont operator optimizes switching between fonts. It does the work of 3 Level 1 operators: findfont, scalefont, and setfont and has been optimized by using a caching mechanism. Benefits: Performance, convenience.