reorganise parser to c++ class

[Jochem Snuverink]

reorganisation of the parser.h and gmad.h into a single class would provide a single entry holder class and reduce the number of globals around. for version 1.0

[Jochem Snuverink]

This has been implemented. There is now a single entry point to all the data, the Parser class. There is still room for improvement, this will come gradually, but the main part has been done, so closing the issue.