alternate indexes implementation

indexes.rb

# leaves around a pointer to the root mapping after use

def indexes(name, options = {}, &block)
  @_mapping_pointer ||= @mapping
  @_mapping_pointer[name] = options
  if block_given?
    previous = @_mapping_pointer
    @_mapping_pointer[name][:type] ||= 'object'
    @_mapping_pointer = @_mapping_pointer[name][:properties] = {}
    yield
    @_mapping_pointer = previous
  end
  @_mapping_pointer[name][:type] ||= 'string'
  self
end