Merge pull request #20 from sargon/config

Skript config code refactoring.
named: Support of zones which are maintained in a git repository.

Some communities maintain there local zone file via git. These changes
make it possible to clone the repo and include the zone file into
the named configuration. This also includes a git hook and a update
script.

The script loops over such repository clones and run 'git pull'. When
changes are pulled in a hook will trigger named to reload its
configuration.
readme: Describe new type ffnord::named::zone
named: Exclude localy mastered zone.
Merge pull request #23 from sargon/dns-zone-exclude

meta: Add ability to exclude dns zones.
Merge pull request #22 from sargon/named-zone-git

Integrate zone file from git repo.
named: make zone exclusion optional and controllable.
meta: Extract common pull/reload flow, use git hook.

Instead of checking for changes, via comparing version hashes, use the
hook mechanic of git.

We still want to be able to trigger the functionality by hand, hence we
encapsulate functionality into seperate function. And made them callable
via parameters. Now we can call for pull or just reload. Which wasn't
possible before.

For further reusability we extract the script flow.
fastd: Use git hook for change detection.

Also apply just emerged flow abstraction and rename autoupdate_fastd_keys into update-fastd-keys.
named: Convert custom zones into common update script format.