Support state diagram transition to child states

[CapinWinky]

For example, this is currently not supported:

state DeviceState {
On --> Off
Off --> On
}
[*] --> Off : Powered
DeviceState --> [*] : Loss of Power

For complicated state diagrams, allowing direct connections between child states of two different parent states could bring major improvements to render readability.

To be frank, maybe compare Mermaid's state machine engine with State Machine Cat