Support ByteOrder.BIG_ENDIAN mode when reading/writing doubles

[niloc132]

The old code in PlayN threw an exception when it attempted to encode/decode Doubles from a ByteBuffer, but at least it was reading the long (which it failed to encode/decode) and handling endian-ness. The new impl (from #3) works, but assumes hardware endian-ness and ByteBuffer.order() match.