toggle the editor with `ctrl-h`

glsl/raymarching.js

  tt.render();
  
  var editor = {};
  editor.visible = true;
  editor.el = document.createElement("textarea");
  editor.el.id = "editor";
  editor.el.value = fragmentShaderSrc;
      displayError(e);
    }
  }
  
  editor.toggle = function() {
    if (editor.visible) {
      editor.el.style.display = "none";
    } else {
      editor.el.style.display = "inherit";
      editor.el.focus();
    }
    editor.visible = !editor.visible;
  }
  
  window.addEventListener('keydown', function(ev) {
    if (ev.ctrlKey && ev.keyCode == 72) {
      ev.preventDefault();
      editor.toggle();
    }
  })
} catch (e) {
  displayError(e);
}