Surface limits to client

[mozcomp]

I know I can access the limit attributes in the response headers if I use the _with_http_info, however, it would be nice to be able to access them as client attributes after a request.

Something like ...

xero_client = XeroRuby::ApiClient.new(credentials: CREDENTIALS)
@invoices = xero_client.accounting_api.get_invoices('').invoices
puts xero_client.daylimit_remaining
=> 4940
puts xero_client.minlimit_remaining
=> 58