Add ncurses, launch shell in gnome-terminal.

Add:
	src/interpreter/shell.c
		-replace lib/keyboard/ with ncurses keyboard-handling functions, for
		cross-platform portability.

	src/interpreter/shell_graphics.(c, h)
		-replace lib/xterm_control/ with ncurses
		-add configureGraphicsShell(), freeGraphicsShell(), to initialize and
		deallocate ncurses.
		-add ability to print error messages, by creating a g_visualBuffer
		inside shell_graphics to contain copies of the lines contained in
		shell.c's g_textBuffer in addition to information printed by the shell
		itself.

	makefile
		-add variable containing flags necessary to launch the engine's shell in
		a gnome-terminal.

Rem:
	lib/
		-remove lib/, which contained the keyboard/ and xterm_control/ libs now
		replaced by ncurses.