Add OSX .DS_Store to .gitignore
Introduce IvoryT, initially as just a Repository Reader
Introduce extra IvoryT operations in a few places
Merge pull request #203 from ambiata/topic/ivoryt-reader

Introduce IvoryT, initially as just a Repository Reader
removed "hole in the middle" funtion when ingesting facts
added the snapshot id to the SnapshotMeta class
removed the hole-in-the-middle for snapshots
cleaned-up the chord code
using as(x) instead of .map(_ => x)
merged with master
fixed the failing test and added the -Ywarn-value-discard flag
split the ingest logic to allow the use of a different importer
use the downcast method for checking the repository type and downcast it
fixed the logic for taking a snapshot incrementally
merged with master