HTMLReporter symbols are inline-block rather than floated

On a very large test suite (8000 specs), a significant amount
of time is spent just drawing the spec dots. Some sort of
worse-than-linear artifact that summons itself only when you
have 8000 floated elements trying to hang out together.

This performance penalty is not seen with inline-block.

In Chrome 29:
  Floated dots: 16.795s
  Inline-block dots: 2.774s

Setting the dots to 'display: none;' takes about the same time
as the inline-block figure, so this is probably a low enough bound
(no need for chunked rendering or who knows what).
Merge pull request #428 from tjgrathwell/htmlreporter-inline-block-dots

Change HTMLReporter symbols to be inline-block instead of floated