add checkpoints with live examples (#890)

Also some minor tweaks

docs/tutorial.md

@@ -408,7 +408,7 @@ as an argument, so it can be reduced to:
   ]),
 ```
 
-Visually, everything is _still_ the same.
+Visually, everything is _still_ the same. If you'd like to see a working example of the code so far, have a look [here](https://codesandbox.io/s/hyperapp-tutorial-step-1-gq662)
 
 Actions
 ---------------------
@@ -439,7 +439,7 @@ const StartEditingFilter = state => ({...state, editingFilter: true})
 ```
 
 Actions are just functions describing transformations of the state.
-This actioin keep everything in the state the same except for `editingFilter`
+This action keeps everything in the state the same except for `editingFilter`
 which it sets to `true`.
 
 When Hyperapp dispatches an action, it replaces the old state with the new
@@ -623,6 +623,8 @@ payload through it, providing the returned value as payload to the action.
 
 > Payload filters are also useful when you need a payload that is a combination of custom data and event data
 
+If you'd like to see a working example of the code so far, have a look [here](https://codesandbox.io/s/hyperapp-tutorial-step-2-5yv34)
+
 Effects
 ----------------------------
 
@@ -838,6 +840,7 @@ When the app loads, and when you change the filter, you should see the spinner a
 > If you aren't seeing the spinner, it might just be happening too fast. Try choking your network speed. In the Chrome
 > browser you can set your network speed to "slow 3g" under the network tab in the developer tools.
 
+If you'd like to see a working example of the code so far, have a look [here](https://codesandbox.io/s/hyperapp-tutorial-step-3-2mmug)
 
 Subscriptions
 -------------------------------------------------------------------
@@ -897,6 +900,8 @@ will start when we check the auto update box, and stop when it is unchecked.
 > may need to implement your own. Refer to the [API reference](). Again, 
 > it is no big deal - just not in scope for this tutorial.
 
+If you'd like to see a working example of the final code, have a look [here](https://codesandbox.io/s/hyperapp-tutorial-step-4-8u9q8)
+
 Conclusion
 ------------------
 
@@ -906,5 +911,5 @@ Along the way you've familiarized yourself with
 the core concepts: _view_, _state_, _actions_, _effects_ & _subscriptions_. And that's really all you need to
 build any web application.
 
-So now, go build your dream app, or browse our [Examples]() for more
+So now, go build your dream app, or browse our [Examples](./examples.md) for more
 inspiration.