MakefileExample: Fix AVR_TOOLS_DIR default

Judging by the default for OS X directly above it and the fact that the current default doesn't work, it seems this should not include the `/bin`.
Merge pull request #237 from bgamari/patch-1

MakefileExample: Fix AVR_TOOLS_DIR default
allows "make clean" to be extended in the user's local makefile to clean
other files out, e.g. backup/git files
Merge pull request #240 from sej7278/master

allows "make clean" to be extended

Fix #239
Fix #240
Add auto-lib.py python script to add included libraries automatically
Merge branch 'master' of https://github.com/sudar/Arduino-Makefile into update
Add automatic lib detection with python script, enhance lib listing output when compiling