Another try at a new logo: hand drawing

I drew the traditional sliced Earth logo on paper and scanned it:

![scan](https://cloud.githubusercontent.com/assets/290082/5332426/4bc03a2c-7e3d-11e4-8de6-508e0815b0f3.jpg)

cleaned it up a bit on Gimp:

![scan-clean](https://cloud.githubusercontent.com/assets/290082/5332427/53a75e78-7e3d-11e4-8dd4-33b632bb469c.png)

Loaded it onto Inkscape and used "Trace bitmap" to make paths that I could edit. 
Added color and some tweaks to the margins, simplifying the paths, etc:

![fatiando-logo](https://cloud.githubusercontent.com/assets/290082/5332436/7986f072-7e3d-11e4-9ac3-5fc9f87c24c1.png)

Here is how  it looks with the text as well:

![fatiando-banner-with-url](https://cloud.githubusercontent.com/assets/290082/5332439/b0fc7aae-7e3d-11e4-82ec-281f499618f1.png)