AZTEC: use algorithm adapted from ZXing for optimized encodation

(ticket #347), props Frank Yellin and Rustam Abdullaev;
   also improve performance of `FAST_MODE`
DATAMATRIX: assert max size on `edges` will fit in unsigned short;
   use MASK for DMRE/SQUARE `option_3` setting
PDF417: assert max size on `edges` will fit in unsigned short
GUI: fix setting AZTEC size and ECC combos if not previously set
manual: fix not mentioning AZTEC re `FAST_MODE`;
  gs1 mode footnote: mention 3940's length; pandoc -> 3.9
test suite: DOTCODE: account for new BWIPP input length guard

backend/tests/testcommon.h

@@ -48,6 +48,7 @@ extern "C" {
 #define ZINT_DEBUG_TEST_PERFORMANCE     256
 #define ZINT_DEBUG_TEST_ZXINGCPP        512
 #define ZINT_DEBUG_TEST_BWIPP_ZXINGCPP  1024
+#define ZINT_DEBUG_TEST_AZTEC_SKIP_ALL  2048
 
 #ifdef ZINT_SANITIZEM /* Suppress clang -fsanitize=memory false positives */
 #define ZINT_TESTUTIL_SANITIZEM_INIT     = {0}