Complete documentation for IWriter

* Remove all usage of MatrixMarket for the output String since the
  string format is determined by the implementing class (may not even be
  a matrix)

src/SparseTransform/Convert/IWriter.cs

@@ -2,13 +2,17 @@
 
 namespace SparseTransform.Convert
 {
+    /// <summary>
+    /// Common interface for writer classes that transform a graph object to a serialized string.
+    /// </summary>
     interface IWriter
     {
         /// <summary>
-        /// transformes the <c>graph</c> in a MatrixMarketString
+        /// Transforms the <c>graph</c> to a string representation.
+        /// The format of String is determined by the implementing class and may not necessarily represent a graph.
         /// </summary>
-        /// <param name="graph"></param>
-        /// <returns>transformed MatrixMarketString</returns>
+        /// <param name="graph">IGraph implementation to transform</param>
+        /// <returns>transformed string</returns>
         public String Write(IGraph graph);