Doc: Add chapter for OpenAL Extension support.

Left todo: once there is a common OpenAL extension registry again,
use that for the al_extension and alc_extension aliases/expansions.

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

doc/openal-support.dox

@@ -0,0 +1,52 @@
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015
+              Vladimír Vondruš <mosra@centrum.cz>
+    Copyright © 2015 Jonathan Hale <squareys@googlemail.com>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+/** @page openal-support OpenAL support state
+@brief List of (un)supported OpenAL features and extensions.
+
+@tableofcontents
+
+@section openal-support-state OpenAL implementation state
+
+The extension implementation is considered complete if all its defined types,
+functions and enum values are exposed through the API.
+
+
+@subsection openal-extension-support Extensions
+
+Extension                                   | Status
+------------------------------------------- | ------
+@al_extension{EXT,double}                   | done
+@al_extension{EXT,float32}                  | done
+
+@subsection openal-extension-support OpenAL Soft Extensions
+
+Extension                                   | Status
+------------------------------------------- | ------
+@alc_extension{SOFTX,HRTF}                  | done
+
+
+*/