Fix github commits json example.

The github API used in the `jsonremote.json` example is no longer available: `https://github.com/api/v2/json/commits/list/escoz/quickdialog/master`.

The new `jsonremote.json` now uses `https://github.com/api/v2/json/commits/list/escoz/quickdialog/master` and has the appropriate bindings for the new commits format.

In addition to the json changes, `QBindingEvaluator.m` was updated as well. The problem is that the "authors" element in some of the responses is null/missing, resulting in an exception when trying to call `[object allKeys]` in `-[QBindingEvaluator bindSection:toProperties:]`. 

The quick fix was to check for an `NSNull` value but I suspect a better solution would be to fail more gracefully when binding in general.