WIP initial tutorials

Thinking about a following structure:

```
Tutorials
 |- Setup
 |- SQL
   |- Installation & Setup
   |- Relations and Sequel
   |- Mappers
     |- Simple mapping
     |- Aggregates
   |- Commands
 |- Rails
   |- Installation & Setup
   |- Directory structure
   |- From AR to ROM
```

/cc @elskwid