ReleaseNotes: Fixed a typo.
frontend: Use sdb_proto_get_int() instead of a custom helper.
frontend: Added support for LISTing services and metrics as well.

When listing objects other than hosts, the returned JSON list will include the
respective type listed below each host object.
store: Added a helper function to parse object type names.
frontend/grammar: Added support for LISTing services and metrics.
sysdbql(7): Updated documentation for the LIST command.
sysdbql(7): Use “SysQL” as the official abbreviation.

This is to avoid that people will call it “SQL”. Thanks to Julian Hein (and
others) for suggesting this.
When querying services/metrics skip hosts without such children.

This takes into account any filters and, thus, might mean that filters have to
be evaluated multiple times: once for determining if there are any children
and then again while serializing the data. This is because filtering happens
during serialization at which point it's too late to skip a host.