This PR implements parsing the resolv.conf file in order to detect system default nameserver configuration. This file is present on most systems and will very likely cover the 90% use case (it is not present on Windows systems). This PR includes some trivial "autodetection" code in the examples to show how this can be used in higher level applications (see also reactphp/socket#90).

This does not implement any other "autodection" mechanisms for other systems. In my opinion, the remainder is best discussed in a separate ticket.

Resolves / closes #29
Supersedes / closes #52, thank you @WyriHaximus
Inspired by #75