VS: Add source file property to specify Windows App deployment location

Add a VS_DEPLOYMENT_LOCATION source file property to specify where to
put files that are part of the package.  For example:

  set_property(SOURCE ${ASSET_FILES} PROPERTY VS_DEPLOYMENT_LOCATION "assets")

Without this, sources marked with VS_DEPLOYMENT_CONTENT cannot be
located properly.

Help/manual/cmake-properties.7.rst

@@ -291,6 +291,7 @@ Properties on Source Files
    /prop_sf/OBJECT_OUTPUTS
    /prop_sf/SYMBOLIC
    /prop_sf/VS_DEPLOYMENT_CONTENT
+   /prop_sf/VS_DEPLOYMENT_LOCATION
    /prop_sf/VS_SHADER_ENTRYPOINT
    /prop_sf/VS_SHADER_MODEL
    /prop_sf/VS_SHADER_TYPE

Help/prop_sf/VS_DEPLOYMENT_LOCATION.rst

@@ -0,0 +1,8 @@
+VS_DEPLOYMENT_LOCATION
+----------------------
+
+Specifies the deployment location for a content source file with a Windows
+Phone or Windows Store application when built with a Visual Studio generator.
+This property is only applicable when using :prop_sf:`VS_DEPLOYMENT_CONTENT`.
+The value represent the path relative to the app package and applies to all
+configurations.

Help/release/3.1.0.rst

@@ -159,6 +159,10 @@ Properties
   to tell the Visual Studio generators to mark content for deployment
   in Windows Phone and Windows Store projects.
 
+* A :prop_sf:`VS_DEPLOYMENT_LOCATION` source file property was added
+  to tell the Visual Studio generators the relative location of content
+  marked for deployment in Windows Phone and Windows Store projects.
+
 * The :prop_tgt:`VS_WINRT_COMPONENT` target property was created to
   tell Visual Studio generators to compile a shared library as a
   Windows Runtime (WinRT) component.