Overhaul of advanced features

Origin of:

- composite types
- one of type
- entity definition
- exclusive properties
- examples folder

Syntax update for:

- one of type
- referencing
- templates properties (variable property name)
Yes, we could. Here are some reason for it: 

1. To get rid of one artificial nesting level (there will be no additional items on that level! 
2. It feels more natural to read (and write it this way) 
3. It essentially simplifies writing of longer descriptions including lists