Merge: Bytes update

Various updates to `Bytes`, added a new escaping method taking into account \u and \x escape sequences

Also added a add_char method to `Bytes` for convenience.

`to_bytes` in Text now has an optional length parameter for those who wish not to rely on `cstring_length` (or did not want to pay the cost) for the length in bytes.

Pull-Request: #1850
Reviewed-by: Jean Privat <jean@pryen.org>