Convert digilines to a mod (not modpack). (#32)

Digilines is probably used by most people in its entirety.

I've retained the ability to disable inventory, rtc, lightsensor and
LCD by the minetest settings "diglines_enable_rtc" etc.. If set to
"false", these components will not be loaded. It is assumed by default
that these are enabled.

In the conversion the digilines_lcd:lcd node was renamed to
digilines:lcd (same for all the other nodes). To retain backwards
compatibility I've provided aliases for each of these nodes.

presetrules.lua

@@ -0,0 +1,15 @@
+digiline.rules = {}
+
+digiline.rules.default = 
+{{x=0,  y=0,  z=-1},
+{x=1,  y=0,  z=0},
+{x=-1, y=0,  z=0},
+{x=0,  y=0,  z=1},
+{x=1,  y=1,  z=0},
+{x=1,  y=-1, z=0},
+{x=-1, y=1,  z=0},
+{x=-1, y=-1, z=0},
+{x=0,  y=1,  z=1},
+{x=0,  y=-1, z=1},
+{x=0,  y=1,  z=-1},
+{x=0,  y=-1, z=-1}}