Windows sockets improvements

This merge request adds features to allow compilation with socket support on MS windows. Mostly it involves using a lot of #ifdef _WIN32 statements where the socket headers and commands for socket functionality differ.

It also disables Nagles algorithm which make significant improvements in socket performance for me when using inet sockets on windows (and no difference on linux).

It also adds a folder 'packaging' in the top level, which is intended to containing scripts to assist with packaing MBDyn for different platforms. At the moment this contains only one subfolder 'mswindows' which contains scripts to cross-compile the windows build from Linux using the M Cross Environment (MXE) tool (see www.mxe.cc and github.com/mxe/mxe). In future I am interested in creating a Flatpak configuration which would also ease distribution on Linux platforms. This could also go in the packaging folder.

I have tested the build on both Linux and windows, running a simple socket example on both platforms successfully.

I rebased this branch to the 'develop' branch before issuing this merge request.