Initial base record class implementation

In reference to: https://github.com/NetSweet/netsuite/pull/129#discussion_r19126261
Adding missing update call to ItemFulfillment
Second pass at implementing a base list class

for sub-list management
Using scriptId instead of internalId in search XML generation

Not sure if this will cause issues with < 2013.2 API versions
Renaming GenericList to Sublist
Adding Sublist support class spec
ItemFulfillmentItemList is using Subclass

First sublist using the Sublist base implementation
The goal is to DRY up the sublist implementation