License header moved to .editorconfig (#632)

* License header moved to .editorconfig

* sln file reverted

.editorconfig

@@ -73,4 +73,8 @@ silk_touch_compact_file_format = true
 [*.{appxmanifest,asax,ascx,aspx,build,config,cs,cshtml,csproj,dbml,discomap,dtd,fs,fsi,fsscript,fsx,htm,html,jsproj,lsproj,master,ml,mli,njsproj,nuspec,proj,props,razor,resw,resx,skin,StyleCop,targets,tasks,vb,vbproj,xaml,xamlx,xml,xoml,xsd}]
 indent_style = space
 indent_size = 4
-tab_width = 4
+tab_width = 4
+
+# License header + warning generated if missing
+file_header_template=Licensed to the .NET Foundation under one or more agreements.\nThe .NET Foundation licenses this file to you under the MIT license.
+dotnet_diagnostic.IDE0073.severity = warning

Silk.NET.sln.DotSettings

@@ -11,9 +11,6 @@
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpCodeStyle/BRACES_FOR_WHILE/@EntryValue">Required</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/XmlDocFormatter/IndentSubtags/@EntryValue">DoNotTouch</s:String>
 	<s:String x:Key="/Default/CodeStyle/CodeFormatting/XmlDocFormatter/IndentTagContent/@EntryValue">DoNotTouch</s:String>
-	<s:String x:Key="/Default/CodeStyle/FileHeader/FileHeaderText/@EntryValue">Licensed to the .NET Foundation under one or more agreements.&#xD;
-The .NET Foundation licenses this file to you under the MIT license.&#xD;
-</s:String>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/Abbreviations/=API/@EntryIndexedValue">API</s:String>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/Abbreviations/=CL/@EntryIndexedValue">CL</s:String>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/Abbreviations/=EGL/@EntryIndexedValue">EGL</s:String>