Add examples and documentation

[marcelog]

More examples are needed for:

1. Explain the structure (supervision trees, workers, what's what and what it does)
2. Set up a basic use (supervision trees, behaviors, etc). Expose every configuration option and behavior available, explain what it's used for, why it's there, and how it's used exactly.
3. Explain the different use cases with record examples (KPL, custom KPL, non-KPL)
4. Explain checkpointing (with and without subrecords)

There is some great doc scattered throughout the sources. These should be exposed in the form of a comprehensive wiki or README so a dev can see upfront what this is all about.