Add a test for '<<' for the proof format mode
Add this test to the uncovered functions for Python and Java
Return placeholder value if Proof object is empty
Add tests for this (and add them to uncovered functions)
This pull requests adds support to get Proofs as proper objects from the API.
To do so it adds an object Proof that encapsulates a ProofNode. Furthermore, it adds a function proofsToString to the Solver object that prints (a vector of) proofs. Finally, it modifies the getProof function of the Solver object to return proofs.
Proof rules are returned as strings.
One thing I don't quite like is that the proof component configuration must be given to both the getProof and proofsToString method and must be the same.