nTox Cleaning and Extension

I added a simple getopt system, to take the "-h" and "-f" flags. -h is to print a simple help message. -f is to specify a custom keyfile for reading and writing to. Because of this change, `load_keys()` now takes a path string as an argument.

I changed the format of the help string, so it should print cleaner now.

`print_friendlist()` is now able to recognize _no_ friends, and print a message accordingly.

`line_eval()` also took `char lines[HISTORY][STRING_LENGTH]` as an argument, then never used it. I removed that.

This also seems to fix issue #280, by setting the idstring array in `main()` to zero.