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: make -f Makefile.linuxarmv6l.cross ReleaseABI or DebugABI

Not sure why I had to target the ABIs to force usage of the custom CC and CXX, but the library compiles like a charm.