Export statement documentation.

test/libsolidity/ASTJSON/documentation_on_statements.sol

@@ -0,0 +1,16 @@
+contract C {
+    // this is not exported
+    uint a;
+    function f() public pure returns (uint x) {
+        // test2
+        for (uint i = 0; i < 20; i++) {
+            // not exported either
+            x *= 2;
+        }
+        // nor is this because they are all
+        // not using the triple-slash
+        return x;
+    }
+}
+
+// ----