Adding simple LaTeX template framework.

This adds a method for taking pre-defined LaTeX templates such as those for academic papers, and allows it to be easily used with MultiMarkdown. This includes one such template (the IEEE conference template) as an example, but more can be added by adding subfolders with the appropriate material.

To use a template, the MultiMarkdown metadata simply has to include:
```
latex template: $template
latex input: mmd-latex-template
latex footer: mmd-latex-template-footer
```

where $template is a directory which includes a `setup.tex` for the body of the template, and a `footer.tex` for the footer.