Clean up headline handling.
Linebreaks; always translate $latex to inline math.

The Wordpress content is formatted assuming that all math is inline
math, and formatting some math as (centered) display math and other
math as inline math at the start of a line just looks strange.
More line break fun.

Turns out the details get tricky - need to be very careful where
we translate line breaks into <br>'s and where we don't.
Math escaping fix.
Insert space after $$ if formula starts with '['

This is necessary for the resulting math markup to parse correctly.
Convert tabs in <pre> blocks to spaces.

Markdown defauls to 4 spaces, browsers normally do 8 spaces,
and I'd rather stay clear off the whole mess entirely.
Started shortcode parser.
Switch to newer blog dump.