You might take a look at progit (http://progit.org/ http://progit.org/) -- it's authored in markdown (github: http://github.com/progit/progit/blob/master/en/01-

You might take a look at progit (http://progit.org/ http://progit.org/) -- it's authored in markdown (github: http://github.com/progit/progit/blob/master/en/01-introduction/01-chapter1.markdown http://github.com/progit/progit/blob/master/en/01-introducti...) which can probably be converted into whatever ebook format you need.