Add an option to close the current tab and select the tab to the left

Add an option to tabs.close to close the current tab
and select the tab to the left.

Bound to `D` by default, which replaces the tabs.close.right
command, which is rarely-used. [1]

The old `D` behavior has been moved to `gd`.

+ update the README and fix some lint errors

[1] https://tinyurl.com/y4mj7hjy

src/content/presenters/ScrollPresenter.ts

@@ -90,7 +90,7 @@ class Scroller {
       clearTimeout(lastTimeoutId);
       lastTimeoutId = null;
     }
-    lastTimeoutId = setTimeout(resetScrolling, 100);
+    lastTimeoutId = window.setTimeout(resetScrolling, 100);
   }
 }