Add support for non-UTF8 attributes

[nitnelave]

Currently, LdapPartialAttributes require the values to be String, i.e. a valid UTF-8 attribute.

However, a fairly common LDAP attribute is JpegPhoto where the raw bytes of the JpegPhoto are sent. It's not representable as a String. It should instead be a OsString or Vec<u8>.

WDYT? If you want this (it would be a breaking change, I understand) I can try to work on a PR, but otherwise I'll just have my own fork.

[Firstyear]

I think you're right, we should represent this as a Vec. I'd be happy to review and help with the PR :)

[Firstyear]

@nitnelave Sorry for the huge delay on this. I'm going to make this change within the week and will update to 0.3 to resolve.