Add dsl for outcome schemas (tables) for roqua

lib/quby/compiler/outputs/roqua_serializer.rb

@@ -77,7 +77,7 @@ module Quby
 
         def outcome_tables_schema
           # hash of tables, with the score keys (rows) and subscore keys (columns) used for each
-          tables = Hash.new{ |hash, key| hash[key] = {score_keys: [], subscore_keys: []} }
+          tables = Hash.new{ |hash, key| hash[key] = {score_keys: Set.new, subscore_keys: Set.new } }
           # hash of `subscore_key: subscore_label` pairs used in tables
           headers = {}
           
@@ -89,9 +89,6 @@ module Quby
             end
           end
           
-          tables.values.each { |table| table[:score_keys].uniq! }
-          tables.values.each { |table| table[:subscore_keys].uniq! }
-          
           {
             headers: headers,
             tables: tables.values,