pagmo 2.3

This release features an important under-the-hood change regarding the serialization backend, where the dill library has been replaced by cloudpickle. cloudpickle should provide a comparable feature set to dill while solving a few issues that were encountered by users in some specific cases (see #106).

A number of documentation fixes and improvements are also included in this new version.

As usual, the full changelog is available at https://esa.github.io/pagmo2/changelog.html.