Initial commit (#419).

src/main/java/org/gitlab4j/api/models/IssueLink.java

+package org.gitlab4j.api.models;
+
+import org.gitlab4j.api.utils.JacksonJson;
+
+public class IssueLink {
+
+    private Issue sourceIssue;
+    private Issue targetIssue;
+
+    public Issue getSourceIssue() {
+        return sourceIssue;
+    }
+
+    public void setSourceIssue(Issue sourceIssue) {
+        this.sourceIssue = sourceIssue;
+    }
+
+    public Issue getTargetIssue() {
+        return targetIssue;
+    }
+
+    public void setTargetIssue(Issue targetIssue) {
+        this.targetIssue = targetIssue;
+    }
+
+    @Override
+    public String toString() {
+        return (JacksonJson.toJsonString(this));
+    }
+}

src/test/resources/org/gitlab4j/api/issue-link.json

+{
+  "source_issue" : {
+    "id" : 83,
+    "iid" : 11,
+    "project_id" : 4,
+    "created_at" : "2016-01-07T12:44:33.959Z",
+    "title" : "Issues with auth",
+    "state" : "opened",
+    "assignees" : [],
+    "labels" : [
+      "bug"
+    ],
+    "author" : {
+      "name" : "Alexandra Bashirian",
+      "state" : "active",
+      "web_url" : "https://gitlab.example.com/eileen.lowe",
+      "id" : 18,
+      "username" : "eileen.lowe"
+    },
+    "updated_at" : "2016-01-07T12:44:33.959Z",
+    "subscribed" : true,
+    "user_notes_count": 0,
+    "web_url": "http://example.com/example/example/issues/11",
+    "confidential": false
+  },
+  "target_issue" : {
+    "id" : 84,
+    "iid" : 14,
+    "project_id" : 4,
+    "created_at" : "2016-01-07T12:44:33.959Z",
+    "title" : "Issues with auth",
+    "state" : "opened",
+    "assignees" : [],
+    "labels" : [
+      "bug"
+    ],
+    "author" : {
+      "name" : "Alexandra Bashirian",
+      "state" : "active",
+      "web_url" : "https://gitlab.example.com/eileen.lowe",
+      "id" : 18,
+      "username" : "eileen.lowe"
+    },
+    "updated_at" : "2016-01-07T12:44:33.959Z",
+    "subscribed" : true,
+    "user_notes_count": 0,
+    "web_url": "http://example.com/example/example/issues/14",
+    "confidential": false
+  }
+}
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src/test/resources/org/gitlab4j/api/linked-issues.json

+[
+  {
+    "id" : 84,
+    "iid" : 14,
+    "issue_link_id": 1,
+    "project_id" : 4,
+    "created_at" : "2016-01-07T12:44:33.959Z",
+    "title" : "Issues with auth",
+    "state" : "opened",
+    "assignees" : [],
+    "labels" : [
+      "bug"
+    ],
+    "author" : {
+      "name" : "Alexandra Bashirian",
+      "state" : "active",
+      "web_url" : "https://gitlab.example.com/eileen.lowe",
+      "id" : 18,
+      "username" : "eileen.lowe"
+    },
+    "updated_at" : "2016-01-07T12:44:33.959Z",
+    "subscribed" : true,
+    "user_notes_count": 0,
+    "web_url": "http://example.com/example/example/issues/14",
+    "confidential": false
+  }
+]
\ No newline at end of file