Quine corners

Quine corners

One of these is used by BQN, but obviously if I'm going to have one I
should have all four.

According to Unicode document L2/07-004, "Proposal to add Medievalist
and Iranianist punctuation characters to the UCS", "The ideally formed
QUINE CORNER (U+231C-U+231F) has equal-length sides and sit at cap
height and on the baseline".  I've tried to implement that here.