Add booktabs package for LaTeX tables

I have been working with simple tables in markdown, and noticed that when converted to LaTeX, some formatting options were embedded in the LaTeX writer, hence impeding me from making any adjustments with just a custom template. For example, the row height and external borders. Why not include the [booktabs] package? This would facilitate the customization of the tables. The defaults produce almost the same results that we already had (with the exception of the top and bottom borders being a bit thicker. This can be adjusted in the `default.latex` template by setting `\setlength\heavyrulewidth{0.4pt}`, however I think the default looks better).

I have also included the header row inside a repetition (i.e. the header row appears on every page).

One thing that is missing it the ability to detect if the caption has been placed on top or at bottom of the table, and place it accordingly in LaTeX document.

[booktabs]: http://www.ctan.org/tex-archive/macros/latex/contrib/booktabs/