+ Complete rewrite of the SQL compiler.
+ Removed SQL staging logic now that GraphQL queries are mapped to
  single SQL queries. It's conceivable we might and to reintroduce this
  later to support non-Postgres DBs.
+ Factored out compiler/interpreter position into a Context type which
  holds path, result path and type.
+ Unique now just converts [T] to T.
+ Removed Project now that multi-step predicate paths are now supported
  correctly.
+ Removed GroupBy query algebra term.
+ Codec/Encoder type parameter removed.
+ Added order independent result testing utility.
+ Added local Docker compose for experimentation.