Add kuzzle info in Document object

[AnthonySendra]

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[codecov-io]

Codecov Report

Merging #200 into 4.x will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              4.x     #200      +/-   ##
==========================================
+ Coverage   99.35%   99.36%   +<.01%     
==========================================
  Files          16       16              
  Lines        1718     1720       +2     
  Branches      458      459       +1     
==========================================
+ Hits         1707     1709       +2     
  Misses         11       11

Impacted Files	Coverage Δ
src/Document.js	100% <100%> (ø)	⬆️
src/Room.js	100% <100%> (ø)	⬆️
src/Collection.js	96.96% <100%> (ø)	⬆️

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[scottinet]

The code looks good to me, but I'm not fond of the kuzzleInfo name. I mean, without context, my first thought is that this property provides informations about Kuzzle.

This also opens a (hopefully quick) discussion on how to name this property in our API (maybe not for the internal storage name, as this name pretty much ensures that there won't be collisions with actual documents).
When documents are exported by our API (and exposed in our SDKs), I think it might be better to rename it for something clearer, like _properties for instance.

[AnthonySendra]

@scottinet totally agree with you. I thought it was a good idea to keep the same name between attribute returned by the API and the attribute returned by the SDK.
Do we have to open an issue on kuzzle side and let this PR in WIP?

The kuzzleInfo attribute is now called meta