[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