Improve documentation generation (pdf only).

Add file VERSION that includes the FLTK version number (only), generate
fltk.pdf with automatic copyright year and doxygen version.


git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10352 ea41ed52-d2ee-0310-a9c1-e6b18d33e121