darioizzo/dcgp: dcgp v1.3

This is the largest dcgp release so far, coming after several months of hard work by the development team. To start off, several changes have been done on dcgp dependencies. In particular: audi v1.7 is now used and that brings in a more efficient generalized dual numbers algebra symengine v0.5.0 is used and interfaced to dcgp to manipulate in c++ directly symbolic expressions represented by CGPs. pagmo v2.11 is now a dependency and used to represents symbolic regression as an optimization problem. Then, we have the first version of a new feature that allows symbolic regression tasks to be solved with a much improved API and algorithms. In particular this involves a new pagmo UPDs (optimization problem) to represents symbolic regression tasks 4 new pagmo UDAs (solution strategies) able to solve the UDP To end, major changes in packaging and distribution are made We dropped support for pip in WIndows, and only kept linux (for the time being) We started and will mainly support conda as a package manager. We started abandoning py27 support (still included in this release, but deprecated) This first release of v1.3 will be followed shortly by one or more point releases aimed at fixing issues we already know of, but that are best tackled once an official release is available of the major version