update doxygen links

Author: jef-n

doc/index.dox

@@ -28,7 +28,9 @@ See \ref api_break for information about incompatible changes to API between rel
 
 Earlier versions of the documentation are also available on the QGIS
 website:
-<a href="http://qgis.org/api/2.8">2.8</a>,
+<a href="http://qgis.org/api/2.12">2.12</a>,
+<a href="http://qgis.org/api/2.10">2.10</a>,
+<a href="http://qgis.org/api/2.8">2.8 (LTR)</a>,
 <a href="http://qgis.org/api/2.6">2.6</a>,
 <a href="http://qgis.org/api/2.4">2.4</a>,
 <a href="http://qgis.org/api/2.2">2.2</a>,