Simplify readme usage example.
We don't actually need coffeescript.

The plugin is compiled by the version bundled with wintersmith.
Perform some text substitutions in code blocks.

This seems not to break anything, so why not?
Support global and file-local markdown extensions.
Remove relative link resolution.

This feature does not seem to be useful at all to me.
Capitalize the PagedownPage class name.

And a few other formatting modifications.
Toss out getIntro and hasMore

These are inherited from MarkdownPage and there's no reason to redefine
them here because they only deal with the converted html, so the
behavior is identical regardless of which markdown renderer is used.
Add some stuff for protecting LaTeX-style math.

I feel dirty committing this.

This removes sections of what appears to be math from pagedown's grubby
hands so, for example, backslashes don't need to be quadruple-escaped.
As this code is stolen from stackoverflow by way of stackedit, I assume
it works acceptably.