Better code formatting

[davestewart]

Would be better if the code in PRE blocks had overflow-x set to scroll (wrapping is fugly and hard to read)

Also, if we use tabs in the gist, please respect that in the PRE! Otherwise it get a bit lumpy.

Ideally you'd ask for each gist or have an option in settings to set the number of spaces.

As a start though (and I know this is debatable) for HTML/PHP 4 spaces per tab is probably the most common.

Many thanks!