added initial version of doxygen documentation

* config-file 'Doxyfile' is created but has to be modified
* doxygen-style comments has to be added
finished doxygen setup

* adjusted Doxyfile (configs)
* added doxygen output to .gitignore
* added 'docs' and 'doxygen' target to Makefile
Merge remote-tracking branch 'origin/master' into feature_doxygen
Changed doxyfiles search path that it finds the sources files
Added simple doxygen documentation for include/main.h
Modified Doxyfile to show private member functions if documented
Added doxygen documentation for AbstractPlotter class
fixed creating own 'createFinalScript()' method in PlotterGnuplot instead of overwriting it
Aggegator Documentation
Minor change

* added dot.
Added doxygen documentation for PlotterGnuplot class
Added doxygen documentation for PlotterPython class
Added doxygen documentation for PlotterR class
Minor changes

* fixed typo in doxygen comment in PlotterPython.h
* added @see link to AbstractPlotter in PlotterGnuplot.h
* placed @file link in the first comment line with /** as convention says
Merge branch 'feature_doxygen' of github.com:schwald/bencho into feature_doxygen
Parameter Documentation
FileWriter Documentation
Printer Documentation and Minor changes
Minor changes on doxygen documentation
updated Doxyfile

* Now shows README.md as Main Page
* Added various graphs to doxygen doc like inheritance and collaboration diagrams