replace double-slash comments with old-skool slash asterisk ones;
define uint16_t etc for Windows ourselves and remove ms_stdint.h &
stdint_msvc.h as no longer used;
(backend (excepting test suite) now C89 compatible)
LICENSE: move from backend to root and move COPYING to frontend, with
copies in frontend_qt & backend_qt, so in where it applies;
add LICENSE section from manual to root README
QRCODE: use stricter interpretation of ZINT_FULL_MULTIBYTE, excluding
certain trailing bytes
libzint: fix some confusing error messages introduced by segment stuff
general: new escape chars \U, \d and \o
backend_qt: fudge rendering of border rectangles due to scaling/translation
rounding errors TODO: better fudge
GUI: foreground/background colours -> text boxes and icon buttons, add swap
button, independently movable picker (NULL parent), preview colour changes,
preview Data Window changes, add clear data (del) buttons, add zap button
and Factory Reset menu option, various other fixes
libzint: remove STATIC_UNLESS_ZINT_TEST, use wrappers
CMake: add find package QtSvg, remove QtXml
manual: split symbology and general specs and sort, move DAFT to 4-state,
UPC/EAN -> EAN/UPC, DataBar -> GS1 DataBar always, expand MAILMARK info,
various other fiddlings
man page: options or -> |, expand MSI Plessey check digit options
README.linux: add packages info
license: add SPDX-License-Identifier to touched files
bmp/emf/ps.c: allow for foreground colour in ULTRA
bmp/gif/pcx.c: allow for BARCODE_STDOUT (fflush/fclose)
emf.c: hexagon rotation field not used; dont't use float index in font loop; Windows stdout binary mode
png.c: remove unused 8-bit; simplify libpng error handling and fclose outfile on error
ps.c: fix buffer overflow on colour_to_pscolor() CMYK
tif.c: fix BLACKISZERO indexes
CODE39: simplify check digit setting
reedsol.c: rs_uint_init_gf() log/alog tables must be zeroed
ZBarcode_Encode: debug: fix access out-of-bounds on non-NUL-terminated source if length < 10
manual.txt/zint.h: document NUL-terminated strings
tests: cover further cases for output (bmp/emf/etc), eci/gb18030/gb2312/sjis, reedsol, AZTEC, CODE39
PLESSEY: add options NCR weighted mod-10, hide check digit(s) in HRT
test suite: now runnable under MSVC 2019, 2017, 2015, MinGW/MSYS
win32/README: update with MSVC 2019 and CMake instructions
