commit 2014.04.27

* Change input type to number for zoom, width and height to address
[issue #2](https://github.com/senlin/so-mobile-map-widget/issues/2) and
adjust FAQ
* Add `format=jpg` to map parameters to allow for the smallest size and
progressive loading of the image
* Fix typo textdomain function
* Move minimum required WP version up to 3.7