Add some details of search API
Add Metastore#keys, #each_key, and #search.
Add x-thingfish header metadata, added 'created' to default metadata.
Adding some experimental code
Ignore integration test dir until the dataset can be pared down
Don't include integration tests in the gem
Implement a few more metadata API methods.

- POST /<uuid>/metadata/<key>
- PUT /<uuid>/metadata/<key>
- Make error messages more consistent.
- Split out testing constants into a seperate file.
Implemented DELETE for the metadata API.
Implement PUT /<uuid>/metadata; add transactional blocks to the stores.