Added linuxarmv6 Makefile and platform variant for cross-compiling for t...

...he raspberry pi using arm-unknown-linux-gnueabi and arm-linux-gnueabihf.

Tested using a raspbian rootfs on:
1. VirtualBox image using Ubuntu Server 12.04 32bit with the official toolchain from https://github.com/raspberrypi/tools
2. Mac OSX 10.7.5 using a toolchain built with the following script: https://github.com/ptoinson/crosstool-arm-osx

Note: the rootfs should have openframeworks codecs and dependecies installed, as well as libc6-dev

Usage:

1. Edit libs/openFrameworksCompiled/project/Makefile following the instructions in it =>
make -j4
2. Edit apps/devApps/raspberrypi_hello_world_gles2/Makefile following the instructions in it => 
make -j4
3. Upload raspberrypi_hello_world_gles2/bin/ to the rpi
4. Run!