Added matlab binding for vector valued constraints

[nicolapiccinelli]

I've added to the mex file the binding for the vector-valued inequality and equality constraints. They are available through the opt structure (in the same way for the standard constraint functions) with the following parameters:

• mfc to define vector-valued inequality function binding
• mfc_count to define the amount of inequality constraints
• mfc_tol to define the tolerance for each inequality constraint
• mh to define vector-valued equality function binding
• mh_count to define the amount of equality constraints
• mh_tol to define the tolerance for each equality constraint

there is also the new callback evaluation function user_mfunction defined with the signature provided in the reference manual. This enhancement allows integrating nlopt as a custom solver for the nonlinear model predictive controller in Matlab (the actual limitation is the need for a double evaluation of the nonlinear constraints function).

The limitation could be avoided by adding another specific binding for inequality-equality function binding (nlmpc custom solver).

[jschueller]

please dont change the indentation or eols, this is annoying to review

[nicolapiccinelli]

please dont change the indentation or eols, this is annoying to review

do you have a vscode profile which can be used?

[jschueller]

no, sorry

[DWolfr]

This should solve #280

[stevengj]

We can use https://github.com/stevengj/nlopt/pull/313/files?w=true to review while ignoring whitespace changes…