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/test/java/sop/util/HexUtilTest.java

@@ -0,0 +1,73 @@
+/*
+ * 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.util;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.nio.charset.Charset;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test using some test vectors from RFC4648.
+ *
+ * @see <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-10">RFC-4648 §10: Test Vectors</a>
+ */
+public class HexUtilTest {
+
+    private static final Charset ASCII = Charset.forName("US-ASCII");
+
+    @Test
+    public void emptyHexEncodeTest() {
+        assertHexEquals("", "");
+    }
+
+    @Test
+    public void encodeF() {
+        assertHexEquals("66", "f");
+    }
+
+    @Test
+    public void encodeFo() {
+        assertHexEquals("666F", "fo");
+    }
+
+    @Test
+    public void encodeFoo() {
+        assertHexEquals("666F6F", "foo");
+    }
+
+    @Test
+    public void encodeFoob() {
+        assertHexEquals("666F6F62", "foob");
+    }
+
+    @Test
+    public void encodeFooba() {
+        assertHexEquals("666F6F6261", "fooba");
+    }
+
+    @Test
+    public void encodeFoobar() {
+        assertHexEquals("666F6F626172", "foobar");
+    }
+
+    private void assertHexEquals(String hex, String ascii) {
+        assertEquals(hex, HexUtil.bytesToHex(ascii.getBytes(ASCII)));
+        assertArrayEquals(ascii.getBytes(ASCII), HexUtil.hexToBytes(hex));
+    }
+}