Remove support for VS2013 (dev12)

This change removes support for Visual Studio 2013. Doing this will
afford us the use of a much wider set of constructs in C++, as more
recent versions of Visual Studio provide full support for C++11.

I'm going to leave this PR open for a week (at least) to invite any
comments about the change that may be out there.

Note: Although this change is to move to support C++11, we could be
a C++14 code base with little extra effort; our minimum versions of
clang (3.9) and VS (dev14) are both sufficient for C++14 support. I
think the only thing holding that back is that we may want to allow
a 4.9 version of GCC.

Build/Chakra.Core.sln

@@ -2,7 +2,7 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
 VisualStudioVersion = 15.0.26228.4
-MinimumVisualStudioVersion = 10.0.40219.1
+MinimumVisualStudioVersion = 14.0.00000.0
 Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "ChakraCore", "..\bin\ChakraCore\ChakraCore.vcxproj", "{EA882C8D-81FC-42FE-ABD5-2666DB933FDB}"
 	ProjectSection(ProjectDependencies) = postProject
 		{1876E800-AD77-48C4-A2F7-E5265F24AC38} = {1876E800-AD77-48C4-A2F7-E5265F24AC38}