Add LabelProvider, rename {=> Structured}ParameterProvider.

Change-Id: Ib4902a35e22d023fc7e8dda4ca73ec2aab50695d
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java
index ae2e7e0..173d9e2 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java
@@ -7,6 +7,22 @@
 import javax.json.JsonObjectBuilder;
 import javax.json.JsonValue;
 
+/**
+ * A simple single key--value pair forming a {@link StructuredParameter}.
+ *
+ * <p>This class is suitable for the common case of logging a key—value pair as parameter to the
+ * {@code *f} family of logging functions on {@link org.jboss.logging.Logger}. For advanced use
+ * cases, provide your own implementation of {@link StructuredParameter}.
+ *
+ * <p>Example:
+ *
+ * <pre>{@code
+ * logger.infof("Application starting.", StructuredParameter.of("version", "1.0"));
+ * }</pre>
+ *
+ * @see Label
+ * @see StructuredParameter
+ */
 public final class KeyValueParameter implements StructuredParameter {
 
   private final String key;