I'm okay moving the Configuration to the end if consistency is more important, but I'd rather have optional arguments on the end, and Configuration shouldn't be optional. I think Configuration should always be present -- at least until #305 (decouple from Hadoop APIs) is done. And maybe we should consider deprecating the other constructors that don't take a Configuration because it's not clear that one is created automatically.

We can also move it in ParquetWriter to make this consistent.