Adding support for native chroots

* if the target arch is the same as the host's, the chroot will be
  initialised as native
* packages can now be configured to be built in a different than the
  native environment
* build roots are no longer initialised when the repo is set up
Fixing a typo
Making repo and package metadata configurable

These new commands are available:

dr config repo key.to.show  # shows the value of the key
dr config repo key value    # sets key to value
dr config repo key ""       # unsets a key
dr config package key value # works for packages too
Fixing an obscure error when parsing the changelog

https://github.com/KanoComputing/kano-repository-manager/issues/26
Changing 'versions' to more accurate 'builds'

dr list versions # is now deprecated
dr push kano-settings -v 1.2.2-1 # will no longer work

https://github.com/KanoComputing/kano-repository-manager/issues/40
Allow force-sync from a new URL

This will be useful for when the repo address has changed.
Adding support for build cleanups

dr cleanup -p <package> -d <date> -n <number>

https://github.com/KanoComputing/kano-repository-manager/issues/27
Bumping version
Merge pull request #43 from KanoComputing/native-chroots

A batch of new features