How to create an Alexa Skill to talk to ThingSpeak for IoT control

If you are just experimenting with Alexa and your own homemade IoT devices, you may be using a cloud service such as ThingSpeak.
Here is a simple example of everything needed to enable your Amazon Echo or similar device to control your devices by talking directly to Alexa.

You can say things like:

Alexa, tell Smart Control to turn on the light
Alexa, ask Smart Control to switch the lamp off
Alexa, open Smart Control
 - light on

and so on.

You can find the code here on GitHub: