Generate Doxyfile and Doxybook from common source file Doxyfile.in.

Now we have less files to edit, and Doxyfile.in is shared with the
CMake generation of Doxyfile and Doxybook.

Besides that two files with FLTK version numbers are now removed (less
work for future version updates).


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@10762 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

.gitignore

@@ -33,6 +33,8 @@
 /documentation/checkers.0
 /documentation/checkers.6
 /documentation/checkers.z
+/documentation/Doxybook
+/documentation/Doxyfile
 /documentation/fltk.0
 /documentation/fltk.3
 /documentation/fltk-config.0