Removed -Werror

-Werror is too pedantic and prevents users to compile with recent
avr-gcc versions.

For example, there are a lot of "variable 'Dummy' set but not used"
warnings in LUFA that should not be treated as errors.
Made PROGMEM const

Recent avr-gcc versions require that PROGMEM variables are declared as
const.
Added teensy2 board

The Teensy 2.0 USB Development Board is a very small, low-cost
board with an ATMEGA32U4 controller. It's available from

  http://www.pjrc.com/teensy/

No additional components are required - all the IEC lines can be
soldered directly to the board.
Added obj and *.elf to .gitignore
Updated .hex files and checked in matching .inf files

All files compiled with

  avr-gcc.exe (AVR_8_bit_GNU_Toolchain_3.4.2_939) 4.7.2

I also checked in the .inf files (why not? they're needed to use the
.hex files)