improve P/S vs P/L choice when have ECI;
add ZINT_DEBUG_TEST dump
AUSPOST: allow variable length data input
DATAMATRIX: do `EXTRA_ESCAPE_MODE` processing up front & check have
non-zero length afterwards;
disallow `READER_INIT` and `EXTRA_ESCAPE_MODE`;
general: add new `z_zero_fill()` func & use;
add new `z_extra_escape_position_fnc1()` helper;
in `z_ct_set_seg_extra_escapes_eci` check position FNC1 whether
or not have ECI
library: escape_char_process: note escaped backslash followed by
caret by passes `EXTRA_ESCAPE_MODE` check
test suite: BWIPP: update to latest; support AUSPOST variants;
process `EXTRA_ESCAPE_MODE` escaping up front
0a3ffc1dc2