updating changelog to latest news.
### Changes in the API
- New solver versions:
- - MathSAT: 5.5.0
+ - MathSAT: 5.5.3 (Nov 20 2018)
- OptiMathSAT: 1.4.0.10
- - Princess: 2017-12-06-assertionless
- - SMTInterpol: 2.1-335-g4c543a5
- - Z3: z3-4.6.0-9-g36204fa
+ - Princess: 2018-12-06-assertionless
+ - SMTInterpol: 2.5-47-gc0546aa
+ - Z3: 4.7.1.0
- Methods for computing a model, unsat core and allsat are moved from
`ProverEnvironment` upwards into `BasicProverEnvironment` and can now also
be used in `InterpolatingProverEnvironment`
