- 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/tests/data/svg/channel_cmyk_nobg.svg

@@ -0,0 +1,24 @@
+<?xml version="1.0" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+   "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg width="46" height="59" version="1.1"
+   xmlns="http://www.w3.org/2000/svg">
+   <desc>Zint Generated Symbol
+   </desc>
+
+   <g id="barcode" fill="#001FCC">
+      <rect x="0.00" y="0.00" width="2.00" height="40.00" />
+      <rect x="4.00" y="0.00" width="2.00" height="40.00" />
+      <rect x="8.00" y="0.00" width="2.00" height="40.00" />
+      <rect x="12.00" y="0.00" width="2.00" height="40.00" />
+      <rect x="16.00" y="0.00" width="2.00" height="40.00" />
+      <rect x="22.00" y="0.00" width="2.00" height="40.00" />
+      <rect x="26.00" y="0.00" width="6.00" height="40.00" />
+      <rect x="38.00" y="0.00" width="2.00" height="40.00" />
+      <rect x="42.00" y="0.00" width="4.00" height="40.00" />
+      <text x="23.00" y="55.40" text-anchor="middle"
+         font-family="Helvetica, sans-serif" font-size="14.0" >
+         123
+      </text>
+   </g>
+</svg>