Add support for read_only queries

[gkorland]

fix #99

[codecov]

Codecov Report

Merging #101 (6957e55) into master (fadc330) will increase coverage by 0.00%.
The diff coverage is 88.88%.

@@           Coverage Diff           @@
##           master     #101   +/-   ##
=======================================
  Coverage   85.24%   85.24%           
=======================================
  Files           9        9           
  Lines         664      671    +7     
=======================================
+ Hits          566      572    +6     
- Misses         98       99    +1     

Impacted Files	Coverage Δ
test.py	98.41% <85.71%> (-0.49%)	⬇️
redisgraph/graph.py	88.32% <100.00%> (ø)

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