papersize variable in the LaTeX template

Adds a variable `papersize` in the LaTeX template which controls, surprise, paper size. Possible values are those the chosen `documentclass` allows.
papersize variable for ConTeXt template

Controls the `papersize` in ConTeXt template. Any valid argument of
`\setuppapersize[...]` descirbed on the [ConTeXt wiki][wiki] works.

[wiki]: http://wiki.contextgarden.net/PaperSetup
Merge pull request #15 from akerbos/patch-1

papersize variable in the LaTeX template
Merge pull request #16 from adityam/master

papersize variable for ConTeXt template
LaTeX, beamer: Use longtable instead of ctable.
Beamer, LaTeX templates: removed enumerate package.
LaTeX, beamer templates: Don't require 'float' package.

AS far as I can see, it isn't needed by anything pandoc does.
epub-page template: removed separate h1 $title$.

The title is now presumed to be the h1 that begins the body
(if there is one).
Removed unnecessary if around pagetitle.
Use pagetitle in title element for epub templates.
EPUB templates:  Use html5 doctype if epub3.
EPUB page template: Add epub (ops) namespace.
EPUB templates:  Added css, highlighting-css, quotes variables.

Removed hardcoded link to stylesheet.css.  Instead, the EPUB writer
now sets the css variable to stylesheet.css.
Removed epub-coverimage.html template.

Also removed TOC stuff from epub-titlepage.html.
Removed epub-titlepage.html.
Incorporated titlepage stuff into epub-page.html.
Split epub-page.html into default.epub and default.epub3.
EPUB templates:  UTF-8, lang variable, meta tags.
Added css to preserve space in <code> tags.

Thanks to Dirk Laurie.
Added tocdepth to latex template.