Delete "vc11" projects and rename "vc10" projects to "vc1x" to signal version independence.

Visual Studio 2010, 2012 and 2013 share the same project file format. The only parameter that separates the versions is a "platform toolset" flag in the project files that can easily be adjusted. It is therefore little in maintaining separate project files for VS2010, VS2012 and VS2013.