Add [broken] conductivity support

It doesn't seem to be solved by using f64

src/render.rs

@@ -55,7 +55,7 @@ impl ColorTermRenderer {
                 //let g = norm_color(cell.ex());
                 //let b = norm_color(cell.ey());
                 //let g = norm_color(curl(cell.ex(), cell.ey()));
-                let g = norm_color(cell.bz() * 3.0e8);
+                let g = norm_color((cell.bz() * 3.0e8) as _);
                 write!(&mut buf, "{}", RGB(r, g, b).paint(square));
             }
             write!(&mut buf, "\n");