CLI: make --mirror available in standard non-batch mode via

new routines `mirror_start()`, `mirror_outfile()` & limit
  substitutions on Unix to backslash (Windows remains the same);
  restrict "borderwidth", "textgap", "vwhitesp", "whitesp" < 100
CODEONE: fix `ceilf()` -> `C1_MULT_CEIL()` in FAST_MODE encodation
  (improves/changes some encodation)
composite: preserve `gs1_verify()` warning using `warn_level` hack;
  fix wrong name `zint_dbar_omnstk_set_height()` ->
  `zint_dbar_stk_set_height()`;
  use new `zint_micropdf_variant()` & `zint_micropdf_expand()`
  routines (see below)
MICROPDF417: move variant determination into new shareable routine
  `zint_micropdf_variant()` & expansion into `zint_micropdf_expand()`
qzint: add helper methods `setbordertypevalue()`,
  `encodedinputmode()`, `encodedoutputoptions()`,
  `ecivaluetoeciindex()` and `eciindextoecivalue()`
dbar: for performance pre-calculate `combins()` as array
coverage: add `malloc()`-type failure testing to AZTEC,
  CONTENT_SEGS, MEMORY_FILE, raster, Reed-Solomon & vector;
  numerous changes to remove unused code and test more branches
common: add `isxdigit()`
general: various code fiddlings
manual: add char names to sequence and batch format char tables;
  mention long options can be shortened (& use "--compliantheight"
  -> "--compliant");
  expand mirror explanation & document substitutions in footnote;
  workaround xecjk putting space after double quote when quoting
  cjk chars & rejig input mode examples;
  workaround html alignment bug in table gs1-enabled symbologies by
  adding extra rh dashes to header cols;
  add "figure nn: " to txt image tags via sed:
  various other small fixes and rephrasings

backend/zint.h

@@ -77,7 +77,7 @@ extern "C" {
         float x, y;         /* Centre */
         float diameter;     /* Circle diameter. Does not include width (if any) */
         float width;        /* Width of circle perimeter (circumference). 0 for fill (disc) */
-        int colour;         /* Zero for draw with foreground colour (else draw with background colour (legacy)) */
+        int colour;         /* Legacy, no longer used (set to 0) */
         struct zint_vector_circle *next; /* Pointer to next circle */
     };
 
@@ -366,7 +366,6 @@ extern "C" {
 #define ZINT_CAP_HRT                0x0001  /* Prints Human Readable Text? */
 #define ZINT_CAP_STACKABLE          0x0002  /* Is stackable? */
 #define ZINT_CAP_EANUPC             0x0004  /* Is EAN/UPC? */
-#define ZINT_CAP_EXTENDABLE         0x0004  /* Legacy */
 #define ZINT_CAP_COMPOSITE          0x0008  /* Can have composite data? */
 #define ZINT_CAP_ECI                0x0010  /* Supports Extended Channel Interpretations? */
 #define ZINT_CAP_GS1                0x0020  /* Supports GS1 data? */
@@ -380,6 +379,9 @@ extern "C" {
 #define ZINT_CAP_COMPLIANT_HEIGHT   0x2000  /* Has compliant height? */
 #define ZINT_CAP_BINDABLE           0x4000  /* Can set row separators? */
 
+/* Legacy capability flag name */
+#define ZINT_CAP_EXTENDABLE         ZINT_CAP_EANUPC
+
 /* The largest amount of data that can be encoded is 4350 4-byte UTF-8 chars in Han Xin Code */
 #define ZINT_MAX_DATA_LEN       17400
 /* Maximum number of segments allowed for (`seg_count`) */