add switch to turn off writing logfiles

[joergbuchwald]

Fixes #27

[codecov]

Codecov Report

Merging #28 (a7ea1fd) into master (b367f45) will decrease coverage by 0.29%.
The diff coverage is 51.85%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   64.29%   64.00%   -0.30%     
==========================================
  Files          18       18              
  Lines        1151     1150       -1     
==========================================
- Hits          740      736       -4     
- Misses        411      414       +3     

Impacted Files	Coverage Δ
ogs6py/ogs.py	79.05% <51.85%> (-0.95%)	⬇️

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