Updates to babeld

This patchset:

- fixes #33 by generating a configuration file for `babeld`
- introduces a slightly different syntax for specfiying interfaces (backward-compatible)
- allows to use any option, as long as it's supported by `babeld` (i.e. valid options are not hardcoded in the init script anymore, all options are simply passed to `babeld`)

It is mostly backward-compatible, with a few caveats.