Generic parameter control through command line arguments of internal RML definitions.

[jgalan]

Perhaps it would be interesting to introduce a generic way to be able to control any parameter through command line.

Doing something like:

restG4 --g4metadata:gdml_file=geometry.gdml --run:outputFileName=output.root

If we achieve something generic, then we could have full freedom. I.e. I could fix also the number of events as follows:

restG4 --g4metadata:Nevents=100

This issue could be transferred to the rest-for-physics/framework , since it might be a generic way to pass arguments, also interesting for restManager or other future executables.

As it was recently discussed in #29

[lobis]

#58 implements some improvements / features to the CLI, but not complete generic parameter initialization, perhaps https://github.com/rest-for-physics/restG4/blob/master/src/Application.cxx#L127 is a good point to start if someone wants to do this.