Clean up stuff around dirty checking
Move stuff around and make relation/tracker private
Add docs for Session::Relation
Simplify Session::Relation
More docs for Session::Relation
Remove Tracker#[]
Add spec for Session::Relation#state
Use shorter form of raising an error
Simplify Session::Environment a little and add docs
Add spec for Session::Relation#identity
Add specs for Session::Relation#new
Fix mutant config
Add docs for Session
Add spec for Session.start
Add specs for Session#flush