fix: Add support for merging files in heads (#17)

Author: jeromelaban

README.md

@@ -28,11 +28,11 @@ Then select the resource dictionaries to be merged:
 </ItemGroup>
 ```
 
-Then add the following block at the end your project library:
+Then add the following block at the end your project library or app:
 
 ```xml
 <Import Project="$(NuGetPackageRoot)uno.xamlmerge.task\$(_Uno_XamlMerge_Task_Version)\build\Uno.XamlMerge.Task.targets"
-        Condition="'$(TargetFramework)' == '' and exists('$(NuGetPackageRoot)\uno.xamlmerge.task\$(_Uno_XamlMerge_Task_Version)')" />
+        Condition="'$(TargetFramework)' == '' and '$(TargetFrameworks)'!='' and exists('$(NuGetPackageRoot)\uno.xamlmerge.task\$(_Uno_XamlMerge_Task_Version)')" />
 ```
 
 The generated file is called `Generated\mergedpages.xaml` by default, but can be overriden as follows:

src/Uno.XamlMerge.Task/build/Uno.XamlMerge.Task.targets

@@ -9,7 +9,7 @@
 	</PropertyGroup>
 
 	<Target Name="GenerateMergedXaml"
-					BeforeTargets="_ComputeTargetFrameworkItems" Condition="'$(TargetFramework)' == ''">
+					BeforeTargets="_ComputeTargetFrameworkItems;BeforeBuild" Condition="'$(TargetFramework)' == '' or '$(TargetFrameworks)'==''">
 		<ItemGroup>
 			<_FilteredXamlMergeInput
 				Include="@(XamlMergeInput)"