Add string stream and binary stream, add text decoding (#570)

* WIP

* Add binary/string streams and text decoding

* Make string collection fallible

* Oops, forgot pretty hex

* Oops, forgot pretty hex

* clippy

crates/nu-command/src/default_context.rs

@@ -111,6 +111,7 @@ pub fn create_default_context() -> EngineState {
         bind_command! {
             BuildString,
             Char,
+            Decode,
             Format,
             Parse,
             Size,