Refactor code structure

Move X.509 and Openpgp operations into custom packages. Implement more
robust input reading. Do not convert []byte to string unnecessarily.

Finish implementation of X.509 CRL creation.

signer/openpgp_ops/operations.go

@@ -0,0 +1,11 @@
+package openpgp_ops
+
+type OpenPGPRoot struct {
+	Name          string
+	SecretKeyRing string
+	Identifier    string
+}
+
+type OpenPGPProfile struct {
+	Name string
+}