[.NET Core] SUPPORT .NET FRAMEWORK >= 4.6 (#547)

Add MSBuild targets for net46 target framework which copy both x86 and
x64 libsodium binaries into corresponding folders. This allows AnyCPU
applications to load the appropriate binary at runtime via
`LoadLibraryEx`.

packaging/dotnet-core/desktop.targets

@@ -0,0 +1,16 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+    <ItemGroup>
+        <None Include="$(MSBuildThisFileDirectory)..\..\runtimes\win7-x86\native\libsodium.dll">
+            <Link>x86\libsodium.dll</Link>
+            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+            <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
+            <Visible>false</Visible>
+        </None>
+        <None Include="$(MSBuildThisFileDirectory)..\..\runtimes\win7-x64\native\libsodium.dll">
+            <Link>x64\libsodium.dll</Link>
+            <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+            <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
+            <Visible>false</Visible>
+        </None>
+    </ItemGroup>
+</Project>

packaging/dotnet-core/libsodium.props

@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <Project>
   <PropertyGroup>
-    <TargetFramework>netstandard1.1</TargetFramework>
+    <TargetFrameworks>netstandard1.1;net46</TargetFrameworks>
     <DisableImplicitFrameworkReferences>true</DisableImplicitFrameworkReferences>
     <NoBuild>true</NoBuild>
     <IncludeBuildOutput>false</IncludeBuildOutput>
@@ -23,5 +23,6 @@
     <Content Include="AUTHORS" PackagePath="" />
     <Content Include="ChangeLog" PackagePath="" />
     <Content Include="runtimes\**\*.*" PackagePath="runtimes\" />
+    <Content Include="build\**\*.*" PackagePath="build\" />
   </ItemGroup>
 </Project>

packaging/dotnet-core/prepare.py

@@ -42,6 +42,7 @@ LINUX = [
 EXTRAS = [ 'LICENSE', 'AUTHORS', 'ChangeLog' ]
 
 PROPSFILE = 'libsodium.props'
+DESKTOPTARGETSFILE = 'desktop.targets'
 MAKEFILE = 'Makefile'
 BUILDDIR = 'build'
 CACHEDIR = 'cache'
@@ -64,6 +65,7 @@ class Version:
     self.projfile = os.path.join(self.builddir, '{0}.pkgproj'.format(PACKAGE))
     self.propsfile = os.path.join(self.builddir, '{0}.props'.format(PACKAGE))
     self.pkgfile = os.path.join(BUILDDIR, '{0}.{1}.nupkg'.format(PACKAGE, self.version))
+    self.desktoptargetsfile = os.path.join(self.builddir, 'build', 'net46', '{0}.targets'.format(PACKAGE))
 
 class WindowsItem:
 
@@ -202,6 +204,11 @@ def main(args):
     for item in items:
       item.make(f)
 
+    f.write('\n')
+    f.write('{0}: {1}\n'.format(version.desktoptargetsfile, DESKTOPTARGETSFILE))
+    f.write('\t@mkdir -p $(dir $@)\n')
+    f.write('\tcp -f $< $@\n')
+
     f.write('\n')
     f.write('{0}: {1}\n'.format(version.propsfile, PROPSFILE))
     f.write('\t@mkdir -p $(dir $@)\n')
@@ -222,6 +229,7 @@ def main(args):
     f.write('{0}:'.format(version.pkgfile))
     f.write(' \\\n\t\t{0}'.format(version.projfile))
     f.write(' \\\n\t\t{0}'.format(version.propsfile))
+    f.write(' \\\n\t\t{0}'.format(version.desktoptargetsfile))
     for item in items:
       f.write(' \\\n\t\t{0}'.format(item.packfile))
     f.write('\n')