Fixed tcphdr.doff calculation.

Changed some pointer arithmetic and some better code comments.
Minor changes in some routines and code fragments of modules.

Now ^C is hidden from the user.

T50 needs GCC 5 or greater.
This release tries to garantee a perfect compilation and don't allow gcc 4.x or lesser version.

Changes on cksum() routine.

With bug fixes

Major bugfixes (see CHANGELOG).

Simplier build system than GNU's.