Remove Automatic Evaluation

- [X] Stop auto eval for Xor
- [X] Stop auto eval for ITE
- [x] Stop auto eval for Not
- [X] to_nnf
- [x] is_nnf
- [X] is_literal for predicates
- [x] Tests
- [x] Documentation
No but the point is that the name `_argset` is optimized in some places to avoid sorting args when unnecessary (I don't remember if this is done in master or only in #2508).