Copy the average length example to the top

And also make it the default. The primary motivation is that
we need to have a simple example for first time visitors.

Author: PetarKirov

index.dd

@@ -30,6 +30,27 @@ $(DIVC intro, $(DIV, $(DIV,
         )
         $(DIVID your-code-here-default,
 $(RUNNABLE_EXAMPLE
+$(RUNNABLE_EXAMPLE_STDIN
+The D programming language
+Modern convenience.
+Modeling power.
+Native efficiency.)
+----
+// Compute average line length for stdin
+void main()
+{
+    import std.range, std.stdio;
+
+    auto sum = 0.0;
+    auto count = stdin.byLine
+        .tee!(l => sum += l.length).walkLength;
+
+    writeln("Average line length: ",
+        count ? sum / count : 0);
+}
+----
+)
+$(EXTRA_EXAMPLE
 $(RUNNABLE_EXAMPLE_STDIN 2.4 plus 2.4 equals 5 for sufficiently large values of 2.)
 ----
 // Round floating point numbers