Simplest possible metadata impl that could work but not very efficient
* Added spec (more of a metadata acceptance test really but it'll do)
* Squashed bugs
* Docs for Container::Metadata
* KeyPrefixer extracted
* Renamed MetadataMarshaller
* Specs for existing behavior
Attempt to save the user from themselves to a degree:
* Assume that the user may prepend X-Container-Meta- when performing a
  container metadata deletion
* Similarly assume they may prepend X-Remove-Container-Meta- when
  performing a metata create/add
* Already add the necessary prefix on their behalf during
  create/add/delete if they didn't do it themselves. Less coding for
  them ideally.x
* Extract method on the wrong-case finder
* Docs
Weird that this is #url and not #url= as there is a #body=
Extract method on metadata extraction from response headers.
Previously, this was defined at the wrong level of abstraction.
Merge pull request #3 from elight/metadata_dumb

Simplest possible metadata impl that could work but not very efficient