There was some undefined behavior to be fixed in the terminal input
parser.
The behavior of flush seems to have change. The fix was to invert '\0'
and std::flush.
The BS key is used to delete the character on the left of the cursor.
The DEL key is used to delete the character on the right of the cursor.
BackSpace was already implemented. This CL implements DEL.
This is related to bug:
https://github.com/ArthurSonzogni/FTXUI/issues/4