Add certificate policy of type any policy id

Add a function for getting the certificate policy. Currently only
"Any Policy" is supported.
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index a8e7523..1b7ea78 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -116,6 +116,7 @@
 add_test_suite(memory_buffer_alloc)
 add_test_suite(mpi)
 add_test_suite(nist_kw)
+add_test_suite(oid)
 add_test_suite(pem)
 add_test_suite(pkcs1_v15)
 add_test_suite(pkcs1_v21)