Update PKGBUILD to reflect that 1.0-dev has been merged with master, amongst other changes.

I have moved the systemd unit file to scripts/arch/shairport.service to reflect that the SysVinit file is in scripts/debian/init.d/. I'm not sure it should be there; I'll leave that up to you.

I have also removed avahi-daemon from being a required dependency (in both the PKGBUILD and the systemd file) to reflect its current status as optional.

After looking at https://bbs.archlinux.org/viewtopic.php?pid=1205357, it appears that the best way to deal with options is to override the ExecStart line in a /etc/systemd/system/shairport.service.d/[SOMETHING].conf file. The previous method used caused issues when using names with spaces (for instance, "Raspberry Pi"). I have added the .install file to help users understand what to do.