- propagate renaming for crate to fastwave_backend

- repair scope printout from example/vcd.rs
 - update and improve instruction for running examples in README

tests/integration_test.rs

@@ -12,7 +12,7 @@ fn parse_all_VCDs() {
     // see if we can parse all signal trees successfully
     for file_name in FILES {
         let file = File::open(file_name).unwrap();
-        let vcd = fastwave::parse_vcd(file);
+        let vcd = fastwave_backend::parse_vcd(file);
 
         if !vcd.is_ok() {
             dbg!(file_name);