Merge pull request #47 from pellucidanalytics/topic/movie-graph-sample

new sample project demonstrating Datomic as a ‘graph database’
WiP: remove implicit db value from queries
make Datomic.database a plain def rather than an implicit

potentially dangerous to silently provide a new database value
Merge pull request #52 from pellucidanalytics/topic/implicit-db

Remove implicit database value from query methods