- zint_symbol->fgcolour & bgcolour buffer lengths extended 10

-> 16 to allow for "C,M,Y,K" comma-separated decimal percentage
  strings
- API/CLI/GUI: allow foreground/background colours to be specified
  as comma-separated decimal "C,M,Y,K" strings where "C", "M" etc.
  are percentages (0-100) (ticket #281, 3rd point)
- output.c: new funcs `out_colour_get_rgb()` & `out_colour_get_cmyk()`
  and use in bmp/emf/gif etc.
- PCX: add alpha support
- GUI: fix fg/gbcolor icon background not being reset on zap
- GUI: Rearrange some Appearance tab inputs (Border Type <-> Width,
  Show Text <-> Font, Text/Font <-> Printing Scale/Size) to flow
  more naturally (hopefully)
- GUI: save button "Save As..." -> "Save..." and add icon
- CLI: add --bgcolor/colour & --fgcolor/colour synonyms

backend/output.h

@@ -1,7 +1,7 @@
 /*  output.h - Common routines for raster/vector */
 /*
     libzint - the open source barcode library
-    Copyright (C) 2020-2022 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2020-2023 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -39,16 +39,37 @@ extern "C" {
 
 #include <stdio.h> /* For FILE */
 
+/* Check colour options are good (`symbol->fgcolour`, `symbol->bgcolour`) */
 INTERNAL int out_check_colour_options(struct zint_symbol *symbol);
+
+/* Return RGB(A) from (well-formed) colour string. Returns 0 if RGB or converted CMYK, 1 if RGBA */
+INTERNAL int out_colour_get_rgb(const char *colour, unsigned char *red, unsigned char *green, unsigned char *blue,
+                unsigned char *alpha);
+/* Return CMYK from (well-formed) colour string. Returns 0 if CMYK, 1 if converted RBG, 2 if converted RGBA */
+INTERNAL int out_colour_get_cmyk(const char *colour, int *cyan, int *magenta, int *yellow, int *black,
+                unsigned char *rgb_alpha);
+
+/* Set left (x), top (y), right and bottom offsets for whitespace */
 INTERNAL void out_set_whitespace_offsets(const struct zint_symbol *symbol, const int hide_text,
                 float *xoffset, float *yoffset, float *roffset, float *boffset, const float scaler,
                 int *xoffset_si, int *yoffset_si, int *roffset_si, int *boffset_si);
+
+/* Set composite offset and main width excluding addon (for start of addon calc) and addon text, returning
+   UPC/EAN type */
 INTERNAL int out_process_upcean(const struct zint_symbol *symbol, int *p_main_width, int *p_comp_xoffset,
                 unsigned char addon[6], int *p_addon_gap);
+
+/* Calculate large bar height i.e. linear bars with zero row height that respond to the symbol height.
+   If scaler `si` non-zero (raster), then large_bar_height if non-zero or else row heights will be rounded
+   to nearest pixel and symbol height adjusted */
 INTERNAL float out_large_bar_height(struct zint_symbol *symbol, int si, int *row_heights_si, int *symbol_height_si);
+
+/* Split UPC/EAN add-on text into various constituents */
 INTERNAL void out_upcean_split_text(int upceanflag, unsigned char text[],
                 unsigned char textpart1[5], unsigned char textpart2[7], unsigned char textpart3[7],
                 unsigned char textpart4[2]);
+
+/* Create output file, creating sub-directories if necessary. Returns `fopen()` FILE pointer */
 INTERNAL FILE *out_fopen(const char filename[256], const char *mode);
 
 #ifdef __cplusplus