Need to decide on how to handle the model composition with the chain models

And some tests

Can also specify them as JSON-formatted string, to make fitting a bit easier, for instance

version 0.14.1

And get the parameters from the class

Closes #27

* Try to break up the C++ interface into smaller chunks

In order to make compilation less RAM intensive

* Inline the makers, also add the other sources

* Tidying up the splitting

Problem was mcx missing sqrt

This reverts commit 23e09bb7.

Recommended by static analysis in Xcode

(no implicit conversion of nlohmann::json to filesystem)