Implement sokoke_resolve_hostname

Implement sokoke_resolve_hostname

sokoke_prefetch_uri is extended take a callback and user data.

sokoke_resolve_hostname is implemented for resolving hostnames
based on a maximum timeout.

sokoke_magic_uri resolves localhost and uris with a / to verify
if there is a local domain, otherwise falls back to search.

Thanks to Andy Kittner <andkit@gmx.de> for input on proceeding
the event loop while resolving asynchronously.