Use inline block for digits

[jared-hughes]

This improves performance in Chrome. Something about the negative margins made Chrome take quadratic time in the layout step. This is part of why 10k element lists were really slow. After this PR, they should take closer to 1 second to render, rather than 1 minute.

The negative margins were the lines below used for digit grouping, like margin-right: @contract-margin; (since contract-margin is -0.009em).

[mikehaverstock]

Have you verified this doesn't change anything meaningful with rendering? We could, for instance, fire off a job to compare a lot of latex rendering to make sure it's pixel perfect. I'm not good enough with css to know why this is obviously only a performance optimization and not going to change layout.

[mikehaverstock]

How did you come up with this?

[jared-hughes]

Removed all the digit classes and saw the performance was good, then bisected what styles could be the culprit to determine that removing the margins would fix up performance. I then brainstormed a few possible alternatives to using margins:

1. padding (nope, doesn't fix performance)
2. width: ... + transform: translateX(...). This required display: inline-block to get the width to apply.
3. padding + display: inline-block (yep, fixes performance)
4. Just display: inline-block (yep, fixes performance)