Added reaction API

src/main/java/org/kohsuke/github/GHReaction.java

@@ -0,0 +1,55 @@
+package org.kohsuke.github;
+
+import java.io.IOException;
+import java.net.URL;
+
+import static org.kohsuke.github.Previews.SQUIRREL_GIRL;
+
+/**
+ * Reaction to issue, comment, PR, and so on.
+ *
+ * @author Kohsuke Kawaguchi
+ * @see Reactable
+ */
+@Preview @Deprecated
+public class GHReaction extends GHObject {
+    private GitHub root;
+
+    private GHUser user;
+    private ReactionContent content;
+
+    /*package*/ GHReaction wrap(GitHub root) {
+        this.root = root;
+        user.wrapUp(root);
+        return this;
+    }
+
+    /**
+     * The kind of reaction left.
+     */
+    public ReactionContent getContent() {
+        return content;
+    }
+
+    /**
+     * User who left the reaction.
+     */
+    public GHUser getUser() {
+        return user;
+    }
+
+    /**
+     * Reaction has no HTML URL. Don't call this method.
+     */
+    @Deprecated
+    public URL getHtmlUrl() {
+        return null;
+    }
+
+    /**
+     * Removes this reaction.
+     */
+    public void delete() throws IOException {
+        new Requester(root).method("DELETE").withPreview(SQUIRREL_GIRL).to("/reactions/"+id);
+    }
+}