also avoid distributive multiplication with floats to lessen chances of
platform variation (#204 ARM-Cortex crash)
- raster.c: Don't allow for text if scale < 1.0
- raster.c: Cast some indexes to (size_t) to allow for large scale
- vector.c: Check malloc()s and return ZINT_ERROR_MEMORY on fail
- raster/vector.c: various var name changes & other code fiddling
- library.c: Check that scale/height/whitespace/border are reasonable values:
scale (0.01-100), height (0-500), whitespace_width/height (0-100),
border_width (0-100)
- CLI: allow both e.g. '-height' and '--height' (getopt_long_only())
- gif.c: fix GIF_ZLW_PAGE_SIZE -> GIF_LZW_PAGE_SIZE
- GUI: allow whitespace/scale to 100
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
