Created release branch for 1.6.0
Merging release-1.6.0 back to develop
version bump
automatic documentation update
Python interface: typemap logic will now look for possible __DMatrix__, SXMatrix__, __MX__ methods when inspecting a python object.
python typemap: respect errors from iterators. Avoids peculiar crash.
Added NLP_LAMBDA_P to NLPSolver outputs, #566
automatic code generation
Correction to 75146827d35a8569e57fd8f387caa25cd18023a1
Consistent input signature of NLPSolver instances, #566