## Module functionality
Module creates route table of three types:
* if is_public has been set to *true* the module creates default route to internet gateway
* if is_public has been set to *false* and *nat_gateway_id* has been specified, module creates default route to NAT gateway
* if is_public has been set to *false* and *nat_gateway_id* hasn't been specified, module does not create a default route.