Base PGPainlessCLI on new sop-java module

* Rename pgpainless-sop -> pgpainless-cli
* Introduce sop-java (implementation-independent SOP API)
* Introduce sop-java-picocli (CLI frontend for sop-java)
* Introduce pgpainless-sop (implementation of sop-java using PGPainless)
* Rework pgpainless-cli (plugs pgpainless-sop into sop-java-picocli)

sop-java/src/main/java/sop/operation/GenerateKey.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2021 Paul Schaub.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package sop.operation;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import sop.Ready;
+import sop.exception.SOPGPException;
+
+public interface GenerateKey {
+
+    /**
+     * Disable ASCII armor encoding.
+     *
+     * @return builder instance
+     */
+    GenerateKey noArmor();
+
+    /**
+     * Adds a user-id.
+     *
+     * @param userId user-id
+     * @return builder instance
+     */
+    GenerateKey userId(String userId);
+
+    /**
+     * Generate the OpenPGP key and return it encoded as an {@link InputStream}.
+     *
+     * @return key
+     */
+    Ready generate() throws SOPGPException.MissingArg, SOPGPException.UnsupportedAsymmetricAlgo, IOException;
+}