[feature] implement Repository Invitations API

fixes #374

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

@@ -0,0 +1,45 @@
+package org.kohsuke.github;
+
+import java.io.IOException;
+import java.net.URL;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+public class GHInvitation extends GHObject {
+    /*package almost final*/ GitHub root;
+
+    private int id;
+    private GHRepository repository;
+    private GHUser invitee, inviter;
+    private String permissions;
+    private String html_url;
+
+    /*package*/ GHInvitation wrapUp(GitHub root) {
+        this.root = root;
+        return this;
+    }
+
+    /**
+     * Accept a repository invitation.
+     */
+    public void accept() throws IOException {
+        root.retrieve().method("PATCH").to("/user/repository_invitations/" + id);
+    }
+
+    /**
+     * Decline a repository invitation.
+     */
+    public void decline() throws IOException {
+        root.retrieve().method("DELETE").to("/user/repository_invitations/" + id);
+    }
+
+    @Override
+    public URL getHtmlUrl() {
+        return GitHub.parseURL(html_url);
+    }
+}

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

@@ -1137,6 +1137,22 @@ public GHLabel createLabel(String name, String color) throws IOException {
                 .to(getApiTailUrl("labels"), GHLabel.class).wrapUp(this);
     }
 
+    /**
+     * Lists all the invitations.
+     */
+    public PagedIterable<GHInvitation> listInvitations() {
+        return new PagedIterable<GHInvitation>() {
+            public PagedIterator<GHInvitation> _iterator(int pageSize) {
+                return new PagedIterator<GHInvitation>(root.retrieve().asIterator(String.format("/repos/%s/%s/invitations", getOwnerName(), name), GHInvitation[].class, pageSize)) {
+                    protected void wrapUp(GHInvitation[] page) {
+                        for (GHInvitation c : page)
+                            c.wrapUp(root);
+                    }
+                };
+            }
+        };
+    }
+
     /**
      * Lists all the subscribers (aka watchers.)
      *

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

@@ -530,6 +530,15 @@ public GHLicense getLicense(String key) throws IOException {
     }
 
     /**
+     * Gets complete list of open invitations for current user.
+     */
+    public List<GHInvitation> getMyInvitations() throws IOException {
+        GHInvitation[] invitations = retrieve().to("/user/repository_invitations", GHInvitation[].class);
+        for (GHInvitation i : invitations) {
+            i.wrapUp(this);
+        }
+        return Arrays.asList(invitations);
+    }
 
     /**
      * This method returns a shallowly populated organizations.