Allow searches to start on an ID other than zero

Some NetSuite objects have negative internal IDs. Without passing a
negative :start_id, the search starts at zero and cannot be overridden.

This is a temporary fix until we determine how to best support this
feature as well as result batching.

lib/netsuite-rest-client.rb

@@ -84,7 +84,7 @@ def search_records(record_type, search_filters, return_columns, options={})
 
       payload = { 'operation'      => 'SEARCH',
                   'record_type'    => record_type,
-                  'start_id'       => 0,
+                  'start_id'       => options.fetch(:start_id, 0),
                   'search_filters' => search_filters,
                   'return_columns' => return_columns }