Added new /illink parameter (#59)

Adding support for the new `/illink` switch, introduced [here](gluck/il-repack@986c1db#diff-3ee934cbb99395b6bc4f805ef4e686e6d80b0b8e1c27d552ed9590eae4f4bb6fR256).

Author: InteXX

ILRepack.Lib.MSBuild.Task/ILRepack.cs

@@ -215,14 +215,19 @@ public virtual string OutputFile
         /// </summary>
         public virtual string RepackDropAttribute { get; set; }
 
+        /// <summary>
+        ///     Merge IL Linker file XML resources from Microsoft assemblies (optional). Same-named XML resources ('ILLink.*.xml') will be combined during merging.
+        /// </summary>
+        public virtual bool MergeIlLinkerFiles { get; set; }
+
         #endregion
 
         #region Public methods
 
         /// <summary>
         ///     Executes ILRepack with specified options.
         /// </summary>
-        /// <returns>Returns true if its successful.</returns>
+        /// <returns>Returns true if it's successful.</returns>
         public override bool Execute()
         {
             var repackOptions = new RepackOptions
@@ -251,7 +256,8 @@ public override bool Execute()
                 PauseBeforeExit = PauseBeforeExit,
                 OutputFile = _outputFile,
                 AllowWildCards = Wildcards,
-                RepackDropAttribute = RepackDropAttribute
+                RepackDropAttribute = RepackDropAttribute,
+                MergeIlLinkerFiles = MergeIlLinkerFiles
             };
 
             repackOptions.AllowedDuplicateNameSpaces.AddRange(