loadUrl enhancements (#134)

`loadUrl` enhancements

- Make `options` parameter optional
- Allow partial overriding of instance options when calling `loadUrl` directly
- Make `requestOptions` optional
- Document `loadUrl` usage and provide examples

tests/lib/util/clone.js

@@ -0,0 +1,17 @@
+var tape = require("tape")
+
+var clone = require("../../../lib/util/clone")
+
+tape("test clone method", function(t) {
+  var obj = {one: 1, two: 2}
+  var cloned = clone(obj)
+
+  t.notEqual(obj, cloned, "cloned object isn't the original object")
+
+  t.same(obj, cloned, "cloned object has the same values as original object")
+
+  cloned.three = 3
+  t.notSame(obj, cloned, "modified cloned object doesn't have the same values as original object")
+
+  t.end()
+})