Escape the arduino IDE, and use a Makefile

There's a very big problem with how the code is currently structured - large chunks of code are duplicated between files. Additionally, most of this code is hardware interface stuff that has undoubtedly been written before. To fix this, libraries should be used.

However, the way arduino handles libraries does not work nicely with version control - we need our library files in the version-controlled directory, but the arduino IDE insists they go elsewhere. We can't just copy them into the directory with the sketch, because we'd need a different copy of each library for each sketch, which is exactly what we were trying to avoid in the first place.

The only way to have library files under version control is to use a different build system

This pull request includes:
 * I2C device libraries from https://github.com/jrowberg/i2cdevlib
 * A makefile from http://ed.am/dev/make/arduino-mk
 * Huge strip-down of the datalogger program attempting to use these libraries