Merge code from others more updated projects

If you want to finish this bootloader (as you say in Readme), this suggestion could be save you many efforts. I've just found some other tftp bootladers very interesting that may interest you too:
https://github.com/codebendercc/Ariadne-Bootloader
https://github.com/per1234/Ariadne-Bootloader
https://github.com/freetronics/arduino-tftpboot

Start with the repository README, then review the three linked TFTP bootloader projects to identify which implementation ideas are relevant to this unfinished Arduino bootloader. The issue does not name files, tests, or a specific change, so completion would require agreeing on scope and acceptance criteria before implementation.

Written by the indexing model from the issue text.