Visual Studio builds: Support Visual Studio 2017

Visual Studio builds: Support Visual Studio 2017

Update the autotools scripts to support Visual Studio 2017 builds by
copying the Visual Studio 2013 projects and updateing the items as
necessary to obtain the Visual Studio 2017 projects.

Note that the format of the toolset string changed, so allow one to
pass in and thus use a custom toolset string, otherwise the default
toolset string will be generated as it was before.

Note also the Visual Studio 2017 aims to be compatible with Visual
Studio 2015 on the CRT level, so binaries built with 2017 should
work without problems with the binaries built with 2015.