Add trim to ZString.

ZString.h

@@ -321,7 +321,13 @@ namespace coreutils {
       ///
       
       ZString goeol();
-      
+
+      ///
+      ///
+      ///
+
+      ZString trim();
+
       ///
       /// Return a block of data as a ZString from the cursor location for
       /// the number of bytes specified by size.