Include offset in return value of #records

Currently, there are 2 modes for retrieving records; pagination on or
off.

If pagination is on (`paginate: true`), we keep making fetch
requests until the response does not include an `offset` for the next
page.

If pagination is off (`paginate: false`), we simply fetch the first page
and stop there.

In order to allow users to control pagination themselves (rather than
simply on or off, as above) we need to provide access to the `offset`
value returned by Airtable.

lib/airrecord/table.rb

@@ -2,6 +2,16 @@
 
 module Airrecord
   class Table
+    class RecordSet < SimpleDelegator
+      attr_reader :records, :offset
+
+      def initialize(records:, offset:)
+        @records = records
+        @offset = offset
+        __setobj__(@records)
+      end
+    end
+
     class << self
       attr_accessor :base_key, :table_name
       attr_writer :api_key
@@ -99,7 +109,7 @@ def records(filter: nil, sort: nil, view: nil, offset: nil, paginate: true, fiel
             ))
           end
 
-          records
+          RecordSet.new(records: records, offset: parsed_response["offset"])
         else
           client.handle_error(response.status, parsed_response)
         end

test/table_test.rb

@@ -37,7 +37,13 @@ def test_walrus_uses_default_key
   end
 
   def test_retrieve_records
-    assert_instance_of Array, @table.records
+    assert_equal 2, @table.records.size
+  end
+
+  def test_records_includes_offset
+    stub_request([{"Name" => "1"}, {"Name" => "2"}], offset: 'dasfuhiu')
+
+    assert_equal 'dasfuhiu', @table.records(paginate: false).offset
   end
 
   def test_different_clients_with_different_api_keys