Increase FD_SETSIZE to 256 for Windows connections

Refactor header and source files to manage the inclusion of `winsock2.h` in a Windows environment. The `FD_SETSIZE` constant is now set to 256, allowing for more simultaneous
connections. Error checks are added in `utiles.h` to ensure `FD_SETSIZE` is defined and correctly set. Update ChangeLog and TODO comments to reflect these changes and their impact on connection limits.

Unmodified 2.1.1 version