<sup>: improve formatting
Add some formatting rules for the <sup> element so that it
formats approximately the same but does not corrupt the line
spacing anymore.
One instance that should not have been using <sup> at all
is just converted to a plain span instead.
With these changes superscripts are still superscripts, they
just no longer cause the line to grow in height thus avoiding
an ugly look on the page where the line with the superscript
has extra space around it.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>