Resolves#410. notcurses_at_yx() accepted a cell*, but the
gcluster of this cell was always set to 0. The EGC is instead
a heap-allocated copy, returned as the primary return value.
This is due to the absence of an egcpool to bind against.
Existing callers can be converted thus:
* instead of passing cell 'c', pass &(c)->attrword, &(c)->channels
* either initialize 'c' with CELL_TRIVIAL_INITIALIZER, or set its
gcluster field to 0 following the call
I've updated all calls from tests/demos, updated the docs, and
updated the C++ and Python wrappers.
* sync up some docs #244
* sync README and man page
* notcurses_output() man page work
* pull attr/channels from output functions #244
* witherworm: clean up explicit moves #244
* still more man page work
* notcurses_lines, last of the man pages i think
* panelreel man page #244
* debian: ruby-ronn->pandoc
* debian: full multiarch compliance
* debian: symbols file
* pandoc: fix syntax for lexgrog
* fm6.mkv: strip audio
* pandoc: fix up apropos man syntax #249
* ncurses_lines man page
