* higher planes stomp wide glyphs
* broken unit test
* develop out widestomp PoC
* fix notcurses_at_yx()
* fix up dig_visible_cell() return value
* refuse wide glyph on last column #242
* set adjacent cell wide when rendering #158
* xray: eliminate weird color flicker
* witherworm: don't eat wide glyphs
* unit test for boxed glyph
* uniblock: no need to emit so many U+200Es
* witherworm: remove wide glyph hack
