new functions and constants for Vdiff

[jmichel7]

Hello, thanks to your nice port of NCurses I have written a console application

https://github.com/jmichel7/Vdiff.jl

Along the way I had to add the curses functions

beep, def_prog_mode, reset_prog_mode, getmouse, mousemask, winch, overwrite, halfdelay, waddstr, addstr

I added also some constants defined in ncurses:

-the file ncurses_mouse.jl contains the definition of the struct M̀EVENT and of the constants used for mouse states.

-the file ncurses_keys.jl contains some of the key definitions in libncurses, to which I have added functions KEY_CTRL and KEY_ALT

You will need to use a version of TextUserInterfaces incorporating the above changes if you want to try Vdiff.
Thank you again for your package!