Fixed small bug in developer doc

The Doxyfile was appended instead of being replaced at any
new generation of the doc

developer-doc/extract

 #!/bin/bash
 
 sed s:@SRCDIR@:"$(echo ../src/*/ ../src/*/*/)": Doxyfile.in|
-sed s:@MAYBE@:NO: >> Doxyfile
+sed s:@MAYBE@:NO: > Doxyfile
 
 cat ../src/*/*cpp |
 awk '