Extensibility: examples

[charlesreid1]

Now that we're doing a deep clean of each class, we have documented a few ideas/situations where you would want to extend the Keymaker or the Shepherd. Now we need to turn these into examples.

Link the examples/ dir with the documentation.

May need to spit documentation for each class into two parts:

• Keymaker
• Extending the Keymaker
• etc.