Comment c++ classes with doxygen

[schalkdaniel]

This is just an add on since it is not very interesting to have this on the R side (user side). But it would be very neat from a developer point of view. The documentation of the C++ wrapper have to be done with roxygen.

[schalkdaniel]

Some Comments:

• A first documentation of C++ code can be viewed by opening man/cpp_man/index.html
• This is now done for the logger class as first try
• Maybe nice to link from the R manual to the C++ manual

List of all files:

• [ ] baselearner
• [ ] compboost
• [x] loss
• [ ] baselearner_factory
• [ ] data
• [x] optimizer
• [ ] baselearner_factory_list
• [x] logger
• [ ] baselearner_track
• [ ] loggerlist