Beamer config

[py]

I created a new format to create Beamer pdf slides:

"Beamer Slides": {
        "scope": {
          "text.html": "html",
          "text.html.markdown": "markdown",
        },
        "pandoc-arguments": [
          "-t", "beamer",
          "--latex-engine=C:/Program Files (x86)/MiKTeX 2.9/miktex/bin/pdflatex.exe"
        ]
      }

I also added beamer to the pandoc-format-file list of extensions, which I believe makes it output a file instead of new buffer.

With the config above, I can generate a latex beamer document, but the ideal case is to create a beamer PDF directly from this command.

The example the pandoc command docs give for creating a beamer pdf:

pandoc -t beamer habits.txt -o habits.pdf

To solve this, there is a need to independently define the file extension in addition to the -t parameter. Some ideas:

1. -t case logic in pandoc.py. If we know all the combos of to formats and desired extensions, we can add some logic in pandoc.py to solve this, e.g. IF t == "beamer", file-ext = "pdf". This would require more specificity within the pandoc-arguments format config file.
2. New config parameter for file extension In addition to the pandoc-arguments parameters, add file-ext to define the extension to stick onto the end of the pandoc command. I think pandoc.py lines 117 to 123 would need to be modified to accommodate this.

[tbfisher]

Excellent, thanks for this. And I see now the need for defaults across transformation definitions as you commented on earlier. I'll work on merging this pull request and add a defaults feature.

[py]

@tbfisher Brian - first of all, thank you for creating this wonderful package. I'm starting to use it again frequently. I imagine you are busy with other things. Is there something I can do to help merge some of these old pull requests and put out a new release? Happy to help.