Move information retrieval to each structure

[lebauce]

Right now, it is not possible to use the library to get only a subset of the information. This PR adds a GetInfo method to every member of the SysInfo struct to allow it. It also has the advantage on making the ordering requirements a bit clearer.

[zcalusic]

Hello @lebauce and thanks for your contribution.

Took me a while to review it, 'cause it changes so much code.

In general, I like it, it does clean things up a bit. Except in one place which I commented above, where I think it complicates things even more. :smile: I don't like that function called with such an ugly conditional from top level, that conditional should stay hidden in the function itself. :smile: