security: rename NO_SIGNATURE error code to MALFORMED_SIGNATURE

And move the documentation for all validation error codes to doxygen

Change-Id: Ibf4b507e3a544f2978192fbfad20cd7dc486818f
diff --git a/tests/unit/security/validation-policy-command-interest.t.cpp b/tests/unit/security/validation-policy-command-interest.t.cpp
index d6fd74f..604c60d 100644
--- a/tests/unit/security/validation-policy-command-interest.t.cpp
+++ b/tests/unit/security/validation-policy-command-interest.t.cpp
@@ -165,7 +165,7 @@
   auto i1 = Interest("/short");
   BOOST_TEST_REQUIRE(i1.getName().size() < signed_interest::MIN_SIZE);
   VALIDATE_FAILURE(i1, "Should fail (not signed / name too short)");
-  BOOST_TEST(lastError.getCode() == ValidationError::NO_SIGNATURE);
+  BOOST_TEST(lastError.getCode() == ValidationError::MALFORMED_SIGNATURE);
 }
 
 BOOST_AUTO_TEST_CASE(BadSigInfo)
@@ -174,7 +174,7 @@
   setNameComponent(i1, command_interest::POS_SIG_INFO, "not-SignatureInfo");
   BOOST_TEST_REQUIRE(i1.getName().size() >= command_interest::MIN_SIZE);
   VALIDATE_FAILURE(i1, "Should fail (signature info is missing)");
-  BOOST_TEST(lastError.getCode() == ValidationError::NO_SIGNATURE);
+  BOOST_TEST(lastError.getCode() == ValidationError::MALFORMED_SIGNATURE);
 }
 
 BOOST_AUTO_TEST_CASE(BadTimestampV02)