doc: add color codes in strings (developer's guide)

doc/asciidoc.conf

@@ -9,4 +9,4 @@
 @k\(([A-Za-z0-9/_&\=])\)=<span class="key">\1</span>
 @k\(([a-z0-9/_&\=][^)]*)\)=<span class="key">\1</span>
 @k\(([^)]+)\)=<span class="key other">\1</span>
-
+@h\(([A-Za-z0-9]+)\)=<span class="hexa">\1</span>

doc/asciidoc.css

@@ -65,3 +65,12 @@ p.table {
 .keyplus {
     font-size: 0.8em;
 }
+.hexa {
+    color: #000077;
+    font-size: 0.85em;
+    font-family: monospace;
+    font-variant: small-caps;
+    border: solid 1px #8888BB;
+    padding: 0 0.2em 0 0.2em;
+    margin: 0 0.2em 0 0.2em;
+}

src/gui/gui-color.h

@@ -20,6 +20,11 @@
 #ifndef __WEECHAT_GUI_COLOR_H
 #define __WEECHAT_GUI_COLOR_H 1
 
+/*
+ * Color from options
+ * (when changing something here, please update the Developer's guide)
+ */
+
 enum t_gui_color_enum
 {
     GUI_COLOR_SEPARATOR = 0,