Function tis620::encode_lossy_buf

pub fn encode_lossy_buf<F>(input: &str, f: F, buffer: &mut Vec<u8>) where
    F: FnMut(char) -> Option<ReplacementChar>, 

Encode arbitrary string as TIS-620, including invalid characters. Writes into the supplied buffer to avoid allocation.

When invalid character is found, call f to get replacement character. If None is returned, silently drop invalid character.