latex template: Added fontfamily variable.

Thanks to tlvince for the patch.  Closes #50.

default.latex

@@ -1,5 +1,9 @@
 \documentclass[$if(fontsize)$$fontsize$,$endif$$if(lang)$$lang$,$endif$$if(papersize)$$papersize$,$endif$$for(classoption)$$classoption$$sep$,$endfor$]{$documentclass$}
+$if(fontfamily)$
+\usepackage{$fontfamily$}
+$else$
 \usepackage{lmodern}
+$endif$
 \usepackage{amssymb,amsmath}
 \usepackage{ifxetex,ifluatex}
 \usepackage{fixltx2e} % provides \textsubscript