NewSchema fix and extended testing for SerializeSchema

[filipecosta90]

Changes included in this PR

• fixes NewSchema ignores opts arg #56
• adds tests for both NewSchema and SerializeSchema

[codecov]

Codecov Report

Merging #58 into master will increase coverage by 2.43%.
The diff coverage is 85.18%.

@@            Coverage Diff             @@
##           master      #58      +/-   ##
==========================================
+ Coverage   72.78%   75.22%   +2.43%     
==========================================
  Files          12       12              
  Lines        1117     1118       +1     
==========================================
+ Hits          813      841      +28     
+ Misses        240      220      -20     
+ Partials       64       57       -7     

Impacted Files	Coverage Δ
redisearch/query.go	81.81% <ø> (+6.93%)	⬆️
redisearch/schema.go	91.91% <85.18%> (+16.36%)	⬆️

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