CMakeLists.txt: cmake min required 3.13 -> 3.5 using CMAKE_REQUIRED_LIBRARIES; add ZINT_COVERAGE option

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

backend/tests/test_gb2312.c

@@ -121,6 +121,7 @@ static void test_gb2312_utf8(int index) {
         /*  6*/ { "―", -1, 0, 1, { 0xA1AA }, "GB2312.TXT mapping" },
         /*  7*/ { "—", -1, 0, 1, { 0xA1AA }, "GB 18030 subset mapping" },
         /*  8*/ { "aβc・·—é—Z", -1, 0, 9, { 'a', 0xA6C2, 'c', 0xA1A4, 0xA1A4, 0xA1AA, 0xA8A6, 0xA1AA, 'Z' }, "" },
+        /*  9*/ { "\200", -1, ZINT_ERROR_INVALID_DATA, -1, {0}, "Invalid UTF-8" },
     };
     int data_size = ARRAY_SIZE(data);
     int i, length, ret;