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
as to fully comply with BSD license (for why Library GPL 2+ not
compatible see https://opensource.stackexchange.com/a/6701),
~3% slower (maybe), +~6K extra in data
(gb18030.c, gb2313.c & sjis.c removed, mapping .TXT files moved
to backend/tools/data & extra ones added, 2 new PHP generators)
GUI: CODE39/EXCODE39: show/hide HIBC check digit option in addition
to enable/disable (less confusing)
CLI: batch: pedantic check for EOF using intChar in newline fgetc()
loop
test_args.c: don't use WIFEXITED(), WEXITSTATUS() on Windows
manual: lessen some copy/paste verbiage by referring back, other
small tweaks/typos
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
