Repl crashes on cyrillic symbol

[DaddyWesker]

Problem occurs on current state of main branch. After cargo test I'm launching repl cargo run --bin metta-repl and after I'm able to input something if I'm inputting cyrillic symbol like ё I'm getting rust panick

> thread 'main' panicked at repl\src\interactive_helper.rs:135:40:
byte index 1 is not a char boundary; it is inside 'ё' (bytes 0..2) of `ё`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: process didn't exit successfully: `target\debug\metta-repl.exe` (exit code: 101)

Probably rust will also panick on other symbols, not only cyrillic.