Add integration specs for PUT Bucket operation
Make the PUT Bucket specs pass.

Definitely needs refactoring. RequestParser is now getting instantiated
twice: once in RackApp, and once in the ObjectStore. ObjectStore is
seeming like an increasingly silly name, given it can now represent a
particular object, or just a particular bucket.

Also, the RequestParser spec isn't testing virtual hosted-style and
CNAME-style requests without a key.

And finally, the README needs updating to reflect the new operation.
Don't instantiate Request multiple times.

All the responsibility for pulling apart the request has moved into
Request (previously RequestParser), and this now gets instantiated
earlier and passed into the operations. This gets rid of the (untested)
EnvHelper.

There are some pending tests for Request that need filling out to cover
some untested behaviour.

Next I'd like to split ObjectStore so responsibilites for buckets and
objects are handled separately.

See the previous commit for further work that's needed.
Update the README with the PUT Bucket operation.
Add a note about *-style operation support.
Further cleaning up of the README.
Make everything RSpec 3 friendly.
Explicitly specify RSpec 3.
Split ObjectStore into BucketOnDisk and ObjectOnDisk.
Fill out missing Request specs.
Complete request parsing specs.