Add pagination support to "users.list" (#182)

* #171 Have each parameter on a dedicated line

This makes it easier to add new ones without exceeding a
readable line length.

* #171 Add optional parameter `cursor` to "users.list"

* #171 Read `next_cursor` from "users.list" response

This allows callers to properly use the pagination of this API method.

* #171 Add support for "limit" parameter of users.list call

SKWebAPI/Sources/WebAPI.swift

@@ -1156,10 +1156,21 @@ extension WebAPI {
         }
     }
 
-    public func usersList(includePresence: Bool = false, success: ((_ userList: [[String: Any]]?) -> Void)?, failure: FailureClosure?) {
-        let parameters: [String: Any] = ["token": token, "presence": includePresence]
+    public func usersList(cursor: String? = nil,
+                          limit: Int? = nil,
+                          includePresence: Bool = false,
+                          success: ((_ userList: [[String: Any]]?, _ nextCursor: String?) -> Void)?,
+                          failure: FailureClosure?) {
+        var parameters: [String: Any] = ["token": token, "presence": includePresence]
+        if let cursor = cursor {
+            parameters["cursor"] = cursor
+        }
+        if let limit = limit {
+            parameters["limit"] = limit
+        }
+
         networkInterface.request(.usersList, parameters: parameters, successClosure: {(response) in
-            success?(response["members"] as? [[String: Any]])
+            success?(response["members"] as? [[String: Any]], (response["response_metadata"] as? [String: Any])?["next_cursor"] as? String)
         }) {(error) in
             failure?(error)
         }