Speed improvements

Changed line drawing algorithm to Bresenham
Rewrote fillCircle algorithm
Added a low level function to write the same pixel data multiple times
First cut of new text print functions

UTFT class is now derived from Print. Proportionally-spaced fonts are
used, with auto kerning.
More changes to text printing

Corrected new text printing functions and added some new ones. Removed
old print functions. Added 10x10 and 16x16 proportional fonts. Removed
old fixed width fonts. Further changes to make code faster and smaller.