Beamer template: In section pages, don't print "Section" and number.

Similarly for parts and subsections.
Reason:  this is not properly internationalized, and for consistency
with other slide formats.

Closes #566.
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).
pulled from pandoc-origin
make dzslides look like my website
removed epub templates which have been superseded
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.