Add parsing of pointers

Pointers can be useful if we want to allow using types recursively
directly (i.e. not as an array or mapping), for example to express
tree structures (decision trees, composite types, etc.).

source/configy/read.d

@@ -822,6 +822,14 @@ package FR.Type parseField (alias FR)
             );
         }
     }
+    else static if (is(FR.Type == T*, T))
+    {
+        // Allocate and parse pointers' values.
+        auto value = new T;
+        *value = node.parseField!(NestedFieldRef!(T, FR))(
+            path, T.init, ctx);
+        return value;
+    }
     else
     {
         static assert (!is(FR.Type == union),

source/configy/test.d

@@ -965,3 +965,21 @@ ds:
     catch (ConfigException exc)
         assert(exc.toString() == "/dev/null(1:11): es.enabled: Expected to be a value of type bool, but is a scalar");
 }
+
+/// Test pointers
+unittest
+{
+    static struct N {
+        @Optional int value;
+        @Optional N* left, right;
+    }
+    auto c = parseConfigString!N(`left:
+  left:
+    value: 1
+right:
+  value: 2
+`, "/dev/null");
+    assert(c.left.left.value == 1);
+    assert(c.left.right is null);
+    assert(c.right.value == 2);
+}