Update to VS2013

SharpYaml.sln

@@ -1,6 +1,8 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 2012
+# Visual Studio 2013
+VisualStudioVersion = 12.0.31010.0
+MinimumVisualStudioVersion = 10.0.40219.1
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{69EE9636-55BA-49C2-827E-D5684221C345}"
 	ProjectSection(SolutionItems) = preProject
 		.gitignore = .gitignore