Concept: major rewrite to handle recent language changes
Dottable/Debugger: reset node numbers for debugging
Query#nodes: make this method public for Concept
TempTable: mild refactor to better memoize #build_it
Define#query: call build rather than ensure_temp_tables
Union: call #from_self on child queries

Ensures that columns forming result rows are preserved
DateRange: derive START/END from observation_period
Filter: add this node
Ndc: Add this drug_exposure node
TrimDateStart/End: add these time operations
To/FromSeerVisits: add these hacky nodes for observations
Except: modify to ignore dates if desired
GraphNodifier: add more types for fake graphs
Dottable: include node number in diagrams
CHANGELOG: update with recent changes