Function encode_str 

pub fn encode_str<'a>(
    input: &[u8],
    output_buffer: &'a mut [u8],
) -> Result<&'a str>

Encode input as base64 into output_buffer and interprets it as a string.

Returns a &str referencing the output_buffer buffer on success or Error::OutOfRange if output_buffer is not large enough.

Using this method avoids having to do unicode checking as it can guarantee that the data written to output_buffer is only valid ASCII bytes.