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
