docs: update doxygen configuration

Most notably:
 - disable OPTIMIZE_OUTPUT_FOR_C, this is a C++ project
 - enable sorting of brief descriptions of class members
 - stop generating documentation for detail headers (not installed)

Change-Id: Ie0608888f53f9b38f0a6e09cf198981cd7474109

wscript

@@ -309,7 +309,7 @@ def doxygen(bld):
             GOOGLE_ANALYTICS=os.getenv('GOOGLE_ANALYTICS', ""))
 
         bld(features="doxygen",
-            doxyfile='docs/doxygen.conf',
+            doxyfile="docs/doxygen.conf",
             use="doxygen-conf")
 
 def sphinx(bld):