Add line-scrolling, shell prompt, gnome-terminal.

Add:
	makefile
		-"make run" now executes bin/engine in a standalone gnome-terminal.
		-add SHELL_TERMINAL variable, containing the flags used to initialize
		gnome-terminal with a name, proper dimensions, etc..

	src/interpreter/shell.c
		-add functional scrolling through command-line history.

	src/interactive_shell/shell_graphics.c
		-add "> " prompt to shell.