- use evdns module
- gethostbyname()
  * check if hostname has no dots; if so, call the standard gethostbyname()
  * same goes if hostname is not of str type
- getaddrinfo():
  * check if host has no dots, not a string or is an IP address; if so, call getaddrinfo()
  * filter out the results based on passed socktype and proto arguments
  * add evdns_flags keyword argument that is passed unchanged to evdns functions
- getnameinfo() is gone; it did not match the original getnameinfo() API at all but
  was a proxy to dns_resolve_reverse(). Since the latter is now available
  in evdns module, this getnameinfo() is not needed
- rename internal variable _ip_re to _ip4_re
- remove unused variable BUFFER_SIZE

- rename wait() to get() (wait is available as an alias for now)
- add switch_args() helper that passes its arguments as a tuple to switch
- __nonzero__() and waiting property are gone
- ready() and successful() methods are added for completeness