Doc: Add al_extension alias.

Signed-off-by: Squareys <Squareys@googlemail.com>

Doxyfile

@@ -277,7 +277,9 @@ ALIASES                = \
     "es_extension2{3}=<a href=\"http://www.khronos.org/registry/gles/extensions/\1/\3.txt\"><tt>\1_\2</tt></a>" \
     "webgl_extension{2}=<a href=\"https://www.khronos.org/registry/webgl/extensions/\1_\2/\"><tt>\1_\2</tt></a>" \
     "fn_al{1}=`al\1()`" \
-    "def_al{1}=`AL_\1`"
+    "def_al{1}=`AL_\1`" \
+    "al_extension{2}=<a href=\"http://icculus.org/alextreg/index.php?operation=op_showext&extname=\1_\2\"><tt>AL_\1_\2</tt></a>" \
+    "alc_extension{2}=<a href=\"http://icculus.org/alextreg/index.php?operation=op_showext&extname=\1_\2\"><tt>ALC_\1_\2</tt></a>"
 
 # This tag can be used to specify a number of word-keyword mappings (TCL only).
 # A mapping has the form "name=value". For example adding "class=itcl::class"