Minor documentation updates

This commit includes a bunch of minor documentation updates, as well
.gitignore changes.
Memory usage summary printed during compilation

When doing a "make" or "make all", the Makefile now prints a memory
usage summary after compilation with avr-size and the util.pl script.

Also changed the boost parameters for the to-spec hack in config.h.
Revised xmas-icetube board (Rev. D)

The xmas-icetube (Rev D) board is currently *untested*, so use this
design at your own risk.  Rev. D includes an enhancement to the
filament driver circuit to increase filament voltage to within
specifications.  The filament voltage issue has been discussed in the
Adafruit Clocks forum:

  http://forums.adafruit.com/viewtopic.php?p=223798#p223798
  http://forums.adafruit.com/viewtopic.php?p=223793#p223793