Support Linux/Avahi properly

[fwcd]

We should make sure that Linux supports actually works as intended with the Avahi stack, given that some additional workarounds might be needed:

• https://stackoverflow.com/questions/7391079/avahi-dns-sd-compatibility-layer-fails-to-run-browse-callback
• https://github.com/nallick/dns_sd/blob/9e9841c131cc1357fc63b69ff75d6d91e45b8429/Sources/dns_sd/DNSService.swift#L146-L170

[Diggory]

Hi, I'm looking for a Bonjour package to use on my Raspberry Pi. I was previously using NetService by Bouke but that seems to crash now and doesn't appear to be maintained any more.

Are you still working on Linux support in this package?

If you aren't, perhaps might you know why NetService is crashing? (Sorry, I'm not familiar with C)
Bouke/NetService#47

Thanks.

[fwcd]

Linux support somewhat depends on upstream (avahi/avahi#18), so someone would have to put some work into polishing up/rebasing/adding tests to that PR before we could progress on #7.