Basic support of ebook building

Requires `pandoc`, `kindlegen` (for mobi) and `pdflatex` (for pdf)
PDF building has some issues – pdflatex complains about fancy unicode symbols. Adding `--latex-engine=xelatex` to pdflatex params helps but it seems now it just skip this fancy symbols. Probably some template [magic](http://stackoverflow.com/questions/18178084/pandoc-and-foreign-characters) should help.
Also some heading adjustment is required – pandoc uses headings to generate TOC, now it looks a little bit clumsy.