Rename and move array normalisation

- Start moving response santisation out of responseparser into new
cleaners file with normaliseResourceArrays -> ensureColections.
- Test cleaners separately and allow passing of collectionPaths
- Rename tests to better describe behaviour
Move renameTextNodes into cleaners
Extract xml namespace cleanup into cleaners
Parse json responses if the content-type is json

- Store reponse headers in cache with response body so that we know how
to parse cached responses
Merge pull request #60 from raoulmillais/handle-json-responses

Handle json responses