Tools for LAMMPS documentation with the "doxygen" documentation platform

are provided.

        New directory: tools/doxygen

        New file:      tools/doxygen/Developer.dox.lammps
        New file:      tools/doxygen/Doxyfile.lammps
        New file:      tools/doxygen/doxygen.sh
        New file:      tools/doxygen/README

The Developer.dox.lammps file contains a slightly revised version of the
Developer.pdf file adopted to the LAMMPS "doxygen" documentation.

The Doxyfile.lammps file is a first proposal for a LAMMPS "doxygen"
documentation flavor and can be adjusted to specific requirements.

The "doxygen.sh" shell script generates the LAMMPS "doxygen"
documentation.

Detailed instructions can be found in the README file.