command line "-h" does not provide a correct description of luminosity options

[itaboada]

This needs to be made consistent with the rewriting of the Luminosity class.

[mlincett]

After the changes by @ChrisCFTung , the **kwargs received by firesong_simulation() are directly passed to get_LuminosityFunction() and get_evolution() (note that in the latter I have implemented the support for parameterised evolutions, that is why now we pass optional arguments here as well). If I am not wrong we lost the configuration string parsing functionality that was previously suggested.

I agree with Chris that firesong_simulation() should receive numerical values for the LF and evo parameters, rather than a configuration string embedding numbers. However, I think the configuration string would still be the best option for the CLI interface.

My suggestion the following:

• firesong_simulation() should take two distinct dictionaries to provide the parameters configuring LF and evolution, that are passed to get_LuminosityFunction() and get_evolution() respectively. I see no good reason to pass an unspecified set of keyword args to both methods and let them deal with parameters that are not meant for them;
• we use configuration strings to provide LF and evolution description to the CLI interface;
• a small parser will translate the configuration strings to the respective dictionaries.

As an alternative, with argparse it could be possible to pass down all unrecognised CLI arguments to firesong_simulation(), leaving free hand to the user, but I think it would become increasingly complicate to input separately the configuration parameters with the command line.

Of course I am fine with any choice as long there's enough consensus :)