Add XML comments to public entities.

Metadata/MediaType.cs

@@ -39,8 +39,16 @@
 #pragma warning disable 612
 namespace Aaru.CommonTypes.Metadata
 {
+    /// <summary>
+    /// Handles media type for metadata
+    /// </summary>
     public static class MediaType
     {
+        /// <summary>
+        /// Converts a media type of a pair of type and subtype strings to use in metadata
+        /// </summary>
+        /// <param name="dskType">Media type</param>
+        /// <returns>Media type and subtype for metadata</returns>
         public static (string type, string subType) MediaTypeToString(CommonTypes.MediaType dskType)
         {
             string discType;