A totally reworked revision!

In order to make it fully battery powered, I've changed out to a 2032 coin cell and removed the switching supplies - even under no load, these can get through an awful lot of current (relatively!). Also changed to a discrete ATmega chip, rather than having the full overhead of a *duino onboard. Boards have been ordered, and should be here pretty soon - once I know they're working, I'll upload the files to GitHub.