Proper vertical centering of text

A common request on Stack Overflow is to vertically centre text in,say, a
circle.  It's a common use case for graphs, maps etc.

Unfortunately there is no satisfactory solution.  Even if/when
`alignment-baseline` and `vertical-align` gets widely supported, they don't
actually provide a perfect solution.

http://jsfiddle.net/ap1dvntt/

Is there a way we can fix this discrepancy?  Perhaps by adding an optional
second argument to `text-anchor` which would control alignment in the
obverse direction?


Paul