removed an unnecessary copy of objects when loading data from source files in memory mode
Revert "removed an unnecessary copy of objects when loading data from source files in memory mode"

This reverts commit 7fdaa1fc46226b9c81d95cd6572a15e41760f98d.
Add AvroSchema#xmap.

Add exponential map to AvroSchema to facilitate instance construction
for custom classes.
set the SimpleDListsSpec as unstable on Travis for now
now _proper_ tagging of the unstable specification