Introduce Page.$ and Page.$$ (#75)

This patch introduces Page.$ and Page.$$ methods which are
aliases for `document.querySelector` and `document.querySelectorAll`. 

Fixes #78.

utils/doclint/test/02-method-errors/doc.md

@@ -1,5 +1,9 @@
 ### class: Foo
 
+#### foo.$()
+
+#### foo.money$$money()
+
 #### foo.proceed()
 
 #### foo.start()

utils/doclint/test/02-method-errors/foo.js

@@ -7,4 +7,10 @@ class Foo {
 
   get zzz() {
   }
+
+  $() {
+  }
+
+  money$$money() {
+  }
 }