Allow additional keys like meta on top level

[anestik]

[codecov-io]

Codecov Report

Merging #11 into master will not change coverage. The diff coverage is 0%.

@@           Coverage Diff           @@
##           master      #11   +/-   ##
=======================================
  Coverage   80.67%   80.67%           
=======================================
  Files           5        5           
  Lines         119      119           
=======================================
  Hits           96       96           
  Misses         23       23

Impacted Files	Coverage Δ
lib/jsonapi/parser/resource.rb	62.5% <0%> (ø)	:arrow_up:

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