TFTP server for Fat16 cards, short filenames.

This is a small TFTP fileserver, using an mmc/sd card for file storage. "Small" means the software does not have an error/retry/timeout mechanism. Tftp Documentation and Tftp RFC.
Attention: filenames are in the 8.3 format and no subdirectories!
A "directory" file named "Dir.txt" containing the directory content of the MMC/SD card is maintained on the card, tftp does not allow to get the card's directory in any other way, it only knows file transfer.
Additionally, file deletion is also present: simply "get" a file with its name preceded with a minus ("-") sign.