Support field naming strategies

[snusnu]

Given the following mapper definition,

register :person do
  map :id,         from: :person_id
  map :account_id, from: :account_id
  map :name,       from: :person_name
end

it should be possible to write it like this:

register :person do
  map :id
  map :account_id, from: :account_id
  map :name
end

[snusnu]

The infrastructure in ramom/entity/* is in place. Next up is a custom NaturalJoin strategy provided by ramom/schema/*.