clarify documentation of getNLPIterations

increase version to 2.2.3

increase version to 2.2.2

increase version to 2.2.1

increase version to 2.2.0

increase version number to 2.1.9

increase version number to 2.1.8

increase version number to 2.1.7

increase version number to 2.1.6

Merge pull request scipopt#271 from SCIP-Interfaces/doxy

Doxy