Use string for RecordType enum value

@Jc2k mentioned this "issue" on the IRC yesterday.

Using integer value for enums is a common practice in Python, but I believe that using a string value is better in this case. It makes debugging and everything else easier.

With this approach, user can also directly pass a string value for `type` argument and it makes getting rid of `RecordType` type in the future easier, if we ever want to do that.