Static ip multi dns

Hi,

Main changes here:
 - get rid of a few dependencies: Netifaces and pkg_resources
 - configure client IPs from a static MAC->IP map, in addition to the normal dynamic allocation pool which can now be disabled
 - allow to send more than one DNS to clients (usually not supported by most clients)

The README should be up-to-date.

Hope this can be of any interest. Please let me know.
Thanks for pybootd!