Update implementation of Tokenizable for Vec<u8>

[ducthotran2010]

The contract call could return uint8[] instead of bytes, but Vec<u8> implementation just supports bytes.

[tomusdrw]

The problem with this is that you will decode Vec<u8> from Token::Array, but encoding (into_tokens) will always return Token::Bytes which is quite misleading.

The split is done on purpose currently (also a bit due to Rust limitations). I think the best way forward would be to introduce a type that looks like this:

pub struct BytesArray(pub Vec<u8>);
impl Tokenizable for BytesArray {
    fn from_token(token: Token) -> Result<Self, Error> {
        match token {
            Token::FixedArray(tokens) | Token::Array(tokens) => {
                Ok(Self(tokens.into_iter().map(Tokenizable::from_token).collect()?))
            }
            other => Err(Error::InvalidOutputType(format!("Expected `Array`, got {:?}", other))),
        }
    }

    fn into_token(self) -> Token {
        Token::Array(self.into_iter().map(Tokenizable::into_token).collect())
    }
}

Unless Token::Bytes and Token::Array have the same ethabi encoding and there is no confusion here (I really don't remember).

Also please add tests.

[tomusdrw]

Awesome, thanks! tiny doc improvement

[tomusdrw]

Thank you!