Problem: grammar had become specific to autoconf

For Malamute service, ac_config and other elements were neither
portable to other build systems, nor abstract:

    <config name = "malamute.cfg" />
    <ac_config name = "src/malamute.service" />
    <other name = "service_file" file = "src/malamute.service"
           dir="@libdir@/systemd/system" />

Solution: replace with 'service = "1"' attribute on main:

    <main name = "malamute" service = "1" />

Which can be interpreted by different platform scripts as needed.
Merge pull request #110 from hintjens/master

Problem: grammar had become specific to autoconf