Add new page to the documentation listing existing LUFA powered projects, fix up some inaccuracies in the documentation.

Makefiles and library modified to add a new F_CLOCK constant to give the unprescaled master input clock frequency, so that the correct PLL mask can be determined even when the CPU (F_CPU) clock rate is prescaled outside the normal input range of the PLL.

Started to clean up the AVRISP Programmer project code, donated by Opendous Inc.