Add acceleration example code
Use floats, not doubles

Doubles are the same as floats on the arduino, so there's no point in using
them.
Add overall acceleration method
Move i2c register #defines into the header file
Add accelerometer register definitions
Neaten up the #defines
Add github url to the top comment
Add comment to raw_to_g
Add comments to rest of the accelerometer methods
Add some better documentation
Add methods to keywords.txt
Add small text about range of bearing()
Add byte to readme
Add description to acceleration
Add units of acceleration
Add note about restarting the IDE
Rename readme.md -> README.md