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
I feel the same way.  I didn't take on any cross-record refactors like that since it would make my PRs dependent on it, but now that they've been mostly merged I can look into creating a base class to DRY up these records.