Enum serialization/deserialization support

[YNNS]

If I deserialize an object from database which has an enum attribute with constructor the deserilization fails.

[thelinuxlich]

Right now the Java driver doesn't have a official mantainer

[NotJustAnna]

Reproduced in 2.4.0 driver.
Fix shouldn't be hard, it's a change in com.rethinkdb.net.Util#convertToPojo, essentially.