porting to ffi-ncurses

I’ve been working on porting the rbcurse gem to ffi-ncurses, since ncurses gems is so so hard to install for a lot of people. Thanks to Sean’s support the work and retesting was actually very little. It’s just that there is a lot of testing to do with all the programs, widgets. Sean is coming out with a version 0.4.0 which I am using. rbcurse 1.3.0 onwards uses ffi-ncurses.