update nightscout web monitor

Howdy,

This is a pull request that allows you to confirm and track updates from the original source back to your version of the code.

Using the green merge button and confirming/accepting the pull request will update your version of the code to match our latest recommendations.  Shortly afterwards, Azure will start updating your website automatically.  Within 10 minutes or so, your website should also update itself automatically.

Here's the effect of this caching code in Azure for the past week:
![nightscout-data-usage-azure](https://cloud.githubusercontent.com/assets/394179/3529816/fc936d72-079d-11e4-8c8e-ed8a4a5b677d.png)

This also includes some other subtle tweaks.  For example, the bg delta is now correctly reported on the pebble watch.  Enjoy. :smile_cat: