update tutorial to the new api. Add some doc about cursors. Add some colors to section 6 (Opening and closing the connection to an X server). Tell me if you want to keep colors or not (colors can be modified in xcb.css)

doc/tutorial/xcb.css

@@ -101,3 +101,23 @@ span.code
   font-family: monospace;
   font-size: 12px;
 }
+pre.code type
+{
+  color: #44bb44;
+}
+pre.code function
+{
+  color: #449fb7;
+}
+pre.code include
+{
+  color: #7d93ae;
+}
+pre.code string
+{
+  color: #ef6e4b;
+}
+pre.code keyword
+{
+  color: #00bbbb;
+}