add QMATRIX

[geoffroyleconte]

Some mps files (including the mps files exported by CPLEX) use the field QMATRIX

[codecov]

Codecov Report

Merging #46 (9d32cc1) into main (92ae300) will increase coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
+ Coverage   84.59%   84.66%   +0.06%     
==========================================
  Files           2        2              
  Lines         461      463       +2     
==========================================
+ Hits          390      392       +2     
  Misses         71       71              

Impacted Files	Coverage Δ
src/readqps.jl	84.22% <ø> (+0.07%)	⬆️

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[dpo]

Thank you!