Add support for certificate policies extension

Add support for certificate policies, as defined in rfc 5280.
Currently support only `anyPolicy` policy.
diff --git a/tests/data_files/test-ca-multi_policy.crt b/tests/data_files/test-ca-multi_policy.crt
new file mode 100644
index 0000000..168e99f
--- /dev/null
+++ b/tests/data_files/test-ca-multi_policy.crt
@@ -0,0 +1,19 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----