Add support for NumberOfThreads

[odow]

Closes #28

[codecov]

Codecov Report

Merging #84 (c2b4e62) into master (28b6a6c) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #84      +/-   ##
==========================================
+ Coverage   82.21%   82.29%   +0.08%     
==========================================
  Files           3        3              
  Lines        1248     1254       +6     
==========================================
+ Hits         1026     1032       +6     
  Misses        222      222              

Impacted Files	Coverage Δ
src/MOI_wrapper.jl	93.10% <100.00%> (+0.04%)	⬆️

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