Handle accents in KaTeX

[gnprice]

From our TeX content survey, at #mobile-team > KaTeX survey results @ 💬, @rajveermalviya writes:

"""

579 messages failed because of unsupported css class: accent.
436 messages failed because of unsupported css class: accent-body.
436 messages failed because of unsupported inline css property: left.

These are related to accents (e.g. $$ \bar{y} $$, $$ \hat{f} $$).

The generated KaTeX HTML and CSS styles for this function does some web specific hacks (like text-align: center + width: 0 and then some left offset), which we have to work around in our parser to get the placement of the accents correct. Especially in the above example where the ^ on f will not be in the top-center of the glyph, but above the top of the (slightly) italicized f.
"""

This was the 4th item after all the functionality included in releases so far (#46 (comment)).