Revert "Let the world know that Sundown is deprecated"

This reverts commit 37728fb2d7137ff7c37d0a474cb827a8d6d846d8.
Removed useless -Wl from .so linking command.
Import the official Markdown 1.0.3 test suite
Use the system specified CC by default
Add MultiMarkdown footnotes extension
Align td and th with css instead of align property

When you align tables with css, <td align="..."> gets overridden.
Using inline styles keeps alignment no matter what CSS contains.