Math needs to be around spacing

[mildsunrise]

On #114 we imposed that math spans be surrounded by spacing (or nothing). This was made to avoid it being interpreted inside words, like so:

go$$rem$$d

But then @gankro observed that cases like:

We know how to solve $$ax + b = 0$$.

wouldn't work because of the dot at the end. So I think that restriction should be left.

[Gankra]

Other similar constructs that become awkward with this rule:

"At the $i$th index..." and "We give each of the $x$'s a..."

The leading space rule doesn't immediately conflict with much I've seen, though. Although maybe if you're going something like "$i$" or ($i$) it could be frustrating.

[uranusjr]

Maybe it is better to remove the constraints altogether to avoid any future problems. It would be pretty frustrating for a user if there’s a case we didn’t consider and is impossible to get around, and we obviously can’t fix it quick enough to help them. And you can always write \$, which would be pretty familiar to users who know LaTeX anyway.

[mildsunrise]

So, we remove the whitespace-around restriction. Any other change needed?

[Gankra]

Only other issue I had was an apparent lack of documentation :P

[mildsunrise]

Heh. Minimal documentation was planned for v3, but for extensions you can always look at hoedown --help and the pertinent PR. ;)

[mildsunrise]

I've hit a minor problem with the current implementation. It's not actually a problem, but it can be unintuitive sometimes. If you write:

\\\\( math \\\\)

This won't produce

<p>\\\( math \\\)</p>

because escapes are not interpreted inside math spans.
Instead, you have to write:

\\\\( math \\\)

[uranusjr]

For the record, there’s another (probably more intuitive) way to get the same output:

\\\\\\( math \\\\\\)

Six backslashes produce \\\. Seven backslashes will also do (the last one escapes the parenthesis after it).