Add a reference makefile, with real-world example
Add `OBJDIR` reference to `arduino-mk-vars.md`

Signed-off-by: tinyladi <ladislas@weareleka.com>
Beautify arduino-mk-vars.md

Clean up markdown and add code blocks where needed

Fix #171
Fix AVR tools paths for chipKIT in Linux.

Fix #175
Fix #174
Fix: Consider usb... to be a valid ISP_PORT

AVRDUDE requires -P usb to be passed as an argument for some ISP
devices, and it is also required in the case where you have multiple
usbtiny or usbasp devices connected at once to select a specific one.

Fix #167
Merge pull request #177 from geoffholden/master

Consider usb... to be a valid ISP_PORT
Add phony target to run pre-build hook script

Fix #176
Add `BOOTLOADER_PARENT` which has to be set if the user sets either of the other two BOOTLOADER variables

Fix #178
replace perl reset script with python one

Fix #180
Fix #127
python3 compatibility
Merge pull request #183 from sej7278/master

python3 compatibility