[Syntax] Use --- instead of nodes{}; net{} nesting blocks

[emil14]

flow Main(start) (stop) {
	Println
	add ReducePort<int> { Add<int> }
	---
	:start -> (
		1 -> add[0]
		2 -> add[1]
	)
	add -> println -> :stop
}

[emil14]

Other ideas were to

1. use def, func or comp (or get back to component) keywords instead of (IMO a little bit confusing flow)
2. Use more Go-like syntax for imports import (...)
3. (Questionable) use () for DI instead of {}

[emil14]

implemented