Add specs for Relation::Aliases::AttributeIndex.build
Add specs for Relation::Aliases::AttributeIndex#entries
Add specs for Relation::Aliases::AttributeIndex#header
Add specs for Relation::Aliases::AttributeIndex#join
Add specs for Relation::Aliases::AttributeIndex#rename
Add specs for Relation::Aliases::AttributeIndex#rename_relations

Fixes the previous implementation which didn't
delete the entry with the old name from the index
Add specs for Relation::Aliases::AttributeIndex#field?
Add specs for Relation::Aliases::AttributeIndex#field
Add specs for Relation::Aliases::AttributeIndex#aliases
Fix specs for Relation::Aliases::AttributeIndex.build

Kills the following mutation:

@@ -1,5 +1,5 @@
 def self.initial_entries(relation_name, attribute_set)
-  attribute_set.primitives.each_with_object({}) do |attribute, entries|
+  attribute_set.each_with_object({}) do |attribute, entries|
     entry = Attribute.build(attribute.field, relation_name)
     entries[entry] = entry
   end
Fix specs for Relation::Aliases::AttributeIndex#join

Kills the following mutation:

@@ -1,4 +1,4 @@
 def strategy
-  @strategy_class.new(self)
+  @strategy_class.new
 end