make sim use proper OOP

sim/compile.lua

@@ -9,15 +9,15 @@ ffi.cdef([[
 ]])
 
 function Simulation.compile(sim)
-	-- assemble a list of all groups
-	local groups = {}
+	-- assemble a list of all nets
+	local all_nets = {}
 	for wire_idx, wire in pairs(sim.wires) do
-		local group = Wire.getgroup(wire)
-		groups[group] = group
+		local net = Wire.getgroup(wire)
+		all_nets[net] = net
 	end
-	local num_groups = 0
-	for group_id, group in pairs(groups) do
-		num_groups = num_groups+1
+	local num_nets = 0
+	for net_id, net in pairs(all_nets) do
+		num_nets = num_nets+1
 	end
 	
 	-- construct each gate into an array