Create Fog::JSON

This is an extraction of `lib/fog/json.rb` from fog@ee091cc

Gem details updated and code cleaned up slightly.
Add minitest and test extracted code works
Bump release version to v1.0.0

The code is very much in use as part of fog so does not really need a
version number hinting it is alpha stage.
MultiJSON uses SemVer so we can track sensibly
Update README
add license/contributing/contributor stuff