Writing Files

Can now write files. Still need to figure out how to terminate. We are
gonna want to upgrade to the full FATFS
Logging Temperature

Not much acutal code has changed since the last commit, but the
fill_zeros funciton in diskio.c now fills 'a's. We need to figure out
how to correctly terminate (and maybe initiate) files.

The main function is now a working temperature logger, and the code has
been tested on the new hardware.
Changes for temp logging