Replace notcurses_render_to_file() and
notcurses_render_to_buffer() with variants that work
on arbitrary piles (the former only worked on the standard
pile). Rewrite the former as trivial wrappers around the
latter, and deprecate the former. Closes#1770.
All our diagnostic macros required a struct notcurses from
which to extract the loglevel. Eliminate this parameter,
and update all caller sites. Add a library-wide (but not
exported) loglevel variable, and set it from both
notcurses_core_init() and ncdirect_core_init(). Add two
new direct mode flags, NCDIRECT_OPTION_VERBOSE and
NCDIRECT_OPTION_VERY_VERBOSE, mapping them to
NCLOGLEVEL_WARNING and NCLOGLEVEL_INFO respectively.
Closes#1690.
ncplane_as_rgba: genericize across blitters
ncplane_as_rgba() previously was implemented explicitly
in terms of NCBLIT_2x1. it now uses the `egcs` field of the
`blitset`. this supports NCBLIT_2x2 and NCBLIT_3x2 in
ncplane_rgba(). Closes#1490.
Writing a partial escape can easily lock up a terminal. This
is especially relevant when working with bitmaps, as they're
thousands or even millions of times longer than a typical
escape. Immediately before writing, block SIGINT, SIGQUIT, and
SIGTERM in the writing thread, and unblock them upon emerging
(at which point we'll immediately see any queued signal
get delivered). Don't block signals like SIGSEGV that would
seem indicative of actual problems. For this to actually work,
all other threads must also have the signals masked; we thus
now add them to the signal mask of notcurses_getc(), rather
than deleting them. Closes#1416.
