Yosys JSON netlist serde structures

Read/write Yosys JSON files in Rust using serde.

Reading

// from a byte slice
let result = Netlist::from_slice(...).unwrap();

// from an io::Read
let result = Netlist::from_reader(reader).unwrap();

Writing

let mut netlist = Netlist::new("Super cool HDL tool");
...
let json = netlist.to_string().unwrap();