roothints: load from zonefile

Loading root hints from zonefile.

• how get root hints? (is it wget and https ok?)
• Can kresd run without root hints? (Only possible configuration to achieve this is remove hints.zone file.)
• roothints can be loaded from file with function roothints('path/to/hints.zone')
• hints module is not needed to run kresd, but to change manually roothints user use hints.root(), maybe this functionality should be in separate builtin module.