Refactoring

[ondrej33]

Refactor the whole project before releasing 0.3.0. The project structure and documentation are improving (hopefully), but we should have a proper look once more functionality is added.

First, finish the refactoring introduced in branch dev-sam-refactoring. Since some of the things were already implemented, and the project changed a lot lately, it would probably be easiest just to check for the changes and directly implement them (instead of merging and making a PR).

Also, there are some further changes to consider:

• Make a struct for typesafe names of variables, propositions, etc. Currently, we utilize strings everywhere, which might cause some readability issues in future.
• Add type aliases or new structs instead of using really complex types, for example, the type used for cache and so on. This should definitely help with the readability.
• In some cases, instead of using structs with public fields, try to rely on public methods.

[ondrej33]

Large part of the issues addressed by #17. Need to refactor further remains.

[ondrej33]

Most of the remaining things relevant for this issue were addressed by 1e893fa and are now integrated in version 0.3.0. The refactoring of some parts would still be nice, but it does not make sense before more new features are added first. Therefore, I am closing this.