Updated readme and fixed error (#4)

* Corrected mistakes

* Fixed error where _parseTimeGrid always returned null

README.md

@@ -18,16 +18,16 @@ The basic tool used to interact with the API is the Session object.
 // .init(server, school, username, password, Optional: useragent)
 Session mySession = await Session.init("demo.server.com", "demo_school", "demo_user", "demo_pass")
 // The ID of the account which credentials you used should now be available over the .userId attribute
-var myId = session.userId;
+var myId = mySession.userId!;
 // Alternatively you can also search for a student
 var myId = (await mySession.searchStudent("demo_forename", "demo_surname"))!.surnameMatches![0].id;
 ```
 Basic methods act just as you expect them to.
 ```dart
 // To get cancellations for a specific day, simply call the .getCancellations method with a startDate
-List<Period> cancellationsTmwr = await mySession.getCancellations(mySession.userId, startDate: DateTime.now().add(Duration(days: 1)));
+List<Period> cancellationsTmwr = await mySession.getCancellations(mySession.userId!, startDate: DateTime.now().add(Duration(days: 1)));
 // The same principle applies to the .getTimetable method, startDate and endDate (inclusive) are optional and will default to the current day
-List<Period> timetable = await mySession.getTimetable(mySession.userId);
+List<Period> timetable = await mySession.getTimetable(mySession.userId!);
 ```
 Some methods like getStudent will cache their result for 30minutes by default.
 ```dart
@@ -41,7 +41,7 @@ mySession.cacheDisposeTime = 60; // Cached values will now stay available for 60
 You want to program a timetable app? These methods might be useful.
 ```dart
 // Get a timegrid that specifies the period time spans for each day
-Timegrid myTimegrid = await mySession.getTimegrid(); 
+TimeGrid myTimeGrid = await mySession.getTimeGrid(); 
 // Get the timetable of the current week
 DateTime mostRecentWeekday(DateTime date, int weekday) => DateTime(date.year, date.month, date.day - (date.weekday - weekday) % 7);
 DateTime monday = mostRecentWeekday(DateTime.now(), DateTime.monday), friday = mostRecentWeekday(DateTime.now(), DateTime.friday);

lib/untis.dart

@@ -185,7 +185,7 @@ class Session {
         var dayDict = rawTimeGrid.firstWhere((element) => (element["day"] == day));
         List<dynamic> dayData = dayDict["timeUnits"];
 
-        List.generate(
+        return List.generate(
             dayData.length,
             (timePeriod) => List.generate(2, (periodBorder) {
                   String border = List.from(["startTime", "endTime"])[periodBorder];
@@ -196,7 +196,6 @@ class Session {
       } else {
         return null;
       }
-      return null;
     }));
   }