Added initial draft of tftp module. Work in progress.
Removed compile errors. Still WIP.

TODO:
- Request, initial handshake
- Implement timeouts
TFTP client is now working (no timeouts).

TODO: Server, timeouts.
Working TFTP client + server. Functional tests.

TODO:
- implement timeout
- unit tests
- manual
Added unit test skeleton for tftp
Reduced complexity of some tftp function
Added TFTP to MODTREE
Added some unit tests for TFTP
TFTP: Timeout implemented. Quality improved via unit tests.
TFTP: Fixed compatibility of put mechanism.

- Added functional tests for put.
- Verified compatibility with tftpd + tftp client (hpa version)
Added user manual for TFTP.