Add TaxType record

https://system.netsuite.com/help/helpcenter/en_US/srbrowser/Browser2014_1/schema/record/taxtype.html
https://system.netsuite.com/help/helpcenter/en_US/Output/Help/SuiteCloudCustomizationScriptingWebServices/SuiteTalkWebServices/TaxType.html
@greggroth  Something I've been considering looking at is creating a `Base` class that implements the initialize method that seems to be copied into each record definition. Thoughts?