Add a color terminal renderer

examples/coremem.rs

@@ -1,5 +1,5 @@
 use coremem::SimState;
-use coremem::render::NumericTermRenderer;
+use coremem::render::ColorTermRenderer;
 use coremem::consts;
 use std::{thread, time};
 
@@ -12,7 +12,7 @@ fn main() {
     state.impulse_b(15, 1.0/consts::C);
     state.impulse_e(15, 1.0);
     loop {
-        NumericTermRenderer.render(&state);
+        ColorTermRenderer.render(&state);
         state.step();
         thread::sleep(time::Duration::from_millis(100));
     }