Don't render % tags or YAML headers

[boardfish]

You can use % tags to set the title and author of the document, or use YAML headers, as follows:

% The Chomsky Hierarchy
% Simon Fish

or

---
title:
- The Chomsky Hierarchy ('56)
author:
- Simon Fish
---

This is compatible with pandoc, especially when used with LaTeX. vim-markdown-composer renders these in either use case, and I don't feel as though it should unless there were a nice way to interpret the information (e.g.)

Title author

.