doc: Updating documentation on format defintion files

src/help/help/files/cmdcfg/csv_format_definition.html

@@ -111,7 +111,8 @@ <h2><a name="generic"></a>Generic commands</h2>
 	<p class="Commanddescription">
 		Specifies names of columns that must be in the data file for it to be loaded. If
 		this is not specified then every column name used to define values in the format
-		definition is assumed to be required unless it is specified as optional.
+		definition is assumed to be required unless there is also a default value where it is
+		used, it is defined as optional (below).
 	</p>
 
 	<p class="Commanddefinition">

src/help/help/general/changelog.html

@@ -12,6 +12,16 @@
 
     <h1><a name="change_log"></a>Change log</h1>
 
+    <h2>Pending release</h2>
+
+    <h3>snap</h3>
+    <p>Bug fix: In a <a href="../files/cmdcfg/csv_format_definition.html">CSV file format definition</a>, if the
+        required columns command is not specified then every column that is
+        referenced in the . is considered required, unless there is also a default for the value it defines. Also
+        added an optional_columns command in a format definition file that allows explicitly specifying that columns
+        are optional.
+    </p>
+
     <h2>Release: Date 2 Apr 2022: 2.8.4</h2>
 
     <h3>concord</h3>