Using sprintf generates a large amount of code. By replacing the
sprintf calls with dedicated code, program size is reduced when
widgets are used.
Also:
- Added a getValLen method for widgets which returns the print
length for the current value, similar to the existing getMaxValLen.
- The value for widgets is now initialised to the minimum value,
instead of 0, because 0 could be outside the specified range.
- Added getValLen and getMaxValLen keywords.
- The MicroViewWidgetDemo example sketch was modified to use
the new getValLen method, plus a few other small changes.
* created MICROVIEWWIDGET class
* added routines to draw widget
* added slider widget
* merged MicroViewWidget into MicroView
* merged SPI.h into MicroView
