Add the necessary input buffer, non-blocking reads, escape trie,
and unit tests to support extended keys, including arrow keys.
Update notcurses-input to print Unicode Control Glyphs instead of
a blank space for control chars.
Slider demo: paint chunks in a pattern, then shuffle them up #72
Right-to-left unit tests #66
Fix up damage to uniblock demo using cup explicit cursor move #66
* cell/ncplane: simplify box API (#97)
* widecolor: use new box api (#97)
* uniblock: use new box API #97
* intro: use new box api #97
* panelreel: use new box api
* boxdemo: use new box API #97
* sliding: use new box API #97
* maxcolor: use new box api #97
* factor out notcurses_channel_prep() #97
* maxcolor: use new channel API #97
* sliding: use new channel API #97
* intro: use new channel API #97
* new output functions with no need for a cell
* add ncplane_putegc() and ncplane_putsimple(). the former takes an EGC, the latter a simple char less than 0x80. (#97)
* cell_prime: directly load all parts of a cell with immediates
* widecolor: use new output API #97
* boxdemo: properly initialize cells
* slider: total time cap of 5 * delaydemo
* maxcolor: use new output API #97
* put stdin into nonblocking mode, retry on short write to stdout #78
* wrap getc_blocking() around a poll #78
* get CCCflag from terminfo. stop clearing the screen in render/startup
* implement ncplane_at_cursor() #76
* ncplane_at_cursor() unit test for simples #76
* PlaneAtCursorComplex unit test #76
* PlaneAtCursorInsane() unit test #76
* nplane_at_cursor: return number of bytes, not just 0/-1
* uniblock-demo: add a bunch of pages from Unicode 12
* demo: make -d delay multiplier a float
* egcpool: check offset against poolsize in check_validity()
* notcurses_init(): set smkx/rmkx to NULL with pass_through_esc
* PlaneAtCursorAttrs unit test #76
* add ncplane_styles() accessor
* sliding: bounding box around puzzle
* slider: make moves, deleting planes #61
* implement z-index move functions
* demo: allow demos to be chosen via command-line option
* allow default bg/fg to be explicitly chosen
* ncplane_resize() unit test #64
* useful links
* slider: use random colors
* use find_above() in ncplace_destroy()
* ncplane_resize() work #64
