Implement `Aliased` for fields

[pmg103]

There is a plugin called Aliased in case you want to rename a field:

serialization_spec = [
  'id',
  'name',
  {'kittehs': Aliased('cats', [
    'name'
  ]}
]

However there’s been an oversight — you can only alias a nested relation like that, not a basic field:

serialization_spec = [
  'id',
  {'title', Aliased('name')},  # DOESN'T WORK
]

For the sake of orthoginality, this form of Aliased, that takes only one argument and renames a field, should be implemented as expected.