SVG Handlebars logo

It changes the Handlebars logo format from PNG to SVG. We could away from using PNG format images by this change.

The new SVG Handlebars logo also has certain style change of look and feel. It's just has a little more flat style.

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Before:
![2014-10-22 at 20 55](https://cloud.githubusercontent.com/assets/34588/4735755/76ea9cec-59e4-11e4-9e80-6bfd478109ed.png)

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After:
![2014-10-22 at 20 54](https://cloud.githubusercontent.com/assets/34588/4735759/7d3aa510-59e4-11e4-928a-8302c8d50862.png)