[avr-libc-dev] More docs: how to use the command-line tools

[Joerg Wunsch]

I finally got sick from digging up in particular the various
machine-specific options for avr-gcc (-mfoo) from the source code over
and over again, so i wrote it all up in a new file named
doc/api/using-tools.dox.  I also added what i thought are useful
options for AVR users, in particular for those users who are plagued
with systems not offering the avr-XXX man and info pages. ;-)

Also, i eventually stumpled again across doc/register-usage.txt, and
integrated it into a true FAQ entry.

All is in CVS now (and register-usage.txt went into the Attic of CVS).
Please review.
-- 
J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/