Step, reset, tick_timer proc and struct cleanup.

Added a tick_timer proc so the code handles the step neatly.
Added some new struct fields to accomodate this and moved danglings
struct defs into the simulator definition.

src/simulator/gui_status_bar.odin

@@ -12,7 +12,7 @@ gui_status_bar :: proc(rect: rl.Rectangle, sim: ^Simulator) {
     cursor: f32 = rect.x + PADDING_X
     cy := rect.y + rect.height * 0.5
 
-    if sim.running && !sim.paused {
+    if !sim.paused {
         status_icon(&cursor, cy, rl.GREEN, .CIRCLE, "Running", sim.font)
     } else {
         status_icon(&cursor, cy, rl.RED, .SQUARE, "Paused", sim.font)