Porting to a new release of FatFs

Current version of FatFs in this directory is 0.13a

Note that new releases are still fairly common -- a couple of times per year.
Here's a guide.

1. The changed contents of the released 'documents' directory can be copied into 'documents'

2. The changed contents of the released 'src' directory can be copied to this base fatFs directory

3. diskio.c is not needed.  Our disk driver is sdPIC32.c, which probably won't need to be changed

4. The new ff.h can be directly used.  Indeed, it needs to be, since it defines the Revision ID
   which is checked by the C code

5. You will need to merge the new ffconf.h to the existing one here. This may only involve the
   "#define FFCONF_DEF" definition.  The old ffconf.h includes the configuration parameters that we
   use for BEDS2, and should remain largely intact, other than FFCONF_DEF.