Update preview less often than at each keystroke

[slel]

Currently, when typing a question or answer, Askbot updates
the preview at each keystroke. When the question or answer
is getting long and/or has a fair amount of inline code or
code blocks and more importantly inline or displayed math
which render using MathJax, this causes a major slowdown.

It might make more sense to update the preview only when
the user stops typing for at least a second.

[slel]

When typing a comment containing math, we can see
some preprocessing going on at each keystroke too,
even though there is no preview!

Can you fix that or hint at the part of the code that
needs fixing so someone can prepare a fix?