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
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
[backend/bmp.c:133]: (error) Memory leak: bitmap
[backend/bmp.c:126]: (error) Memory leak: bitmap
[backend/composite.c:464]: (error) Array index -1 is out of bounds.
[backend/composite.c:507]: (error) Array index -1 is out of bounds.
[backend/dmatrix.c:962]: (style) Redundant condition: i!=0. 'i==0 || (i!=0 && binary[i-1]!='b')' is equivalent to 'i==0 || binary[i-1]!='b''
[backend/raster.c:122]: (error) Memory leak: rotated_pixbuf
[backend/raster.c:506]: (error) Memory leak: pixelbuf
[frontend/main.c:273]: (error) Uninitialized variable: format_string
[frontend_qt/exportwindow.cpp:103]: (style) Array index 'j' is used before limits check.
