Refactor app/adapters

[dazza-codes]

While looking at app/adapters/adapter.rb and app/adapters/abstract_adapter.rb, it seems they could be combined into one class, unless there is a design pattern involved? Also, it's not entirely clear why the abstract_adapter.rb requires both class and instance methods (it seems lines 50-57 try to create instance methods that delegate to class methods for :simple_maps and :to_maps, but they seem to be instance methods already in adapter.rb).

Adapter#map_to_public is not fully covered by unit tests.

Extracted this issue from #77

[dazza-codes]

The AbstractAdapter#to_public_hash seems to be memoized, but that could prevent field additions or deletions from showing up? Perhaps it should not be memoized?

The #to_json instance method calls a class method, i.e.

  def to_json(options = {})
    return self.to_public_hash.to_json(options)
  end

It seems it could be calling an instance method, i.e.

  def to_json(options = {})
    to_public_hash.to_json(options)
  end

This method is not covered by unit tests (looking at simplecov report). Also, the rhs return value from AbstractAdapter#merge_strategy is not covered by unit tests.