Add --backend-param (-b) option for analyze, eval, evaldir commands. …

[osma]

…Fixes #75

[codecov]

Codecov Report

Merging #78 into master will increase coverage by 0.26%.
The diff coverage is 98.63%.

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
+ Coverage   96.29%   96.55%   +0.26%     
==========================================
  Files          28       28              
  Lines        1079     1133      +54     
==========================================
+ Hits         1039     1094      +55     
+ Misses         40       39       -1

Impacted Files	Coverage Δ
tests/test_cli.py	100% <100%> (ø)	⬆️
annif/cli.py	93.1% <100%> (+0.87%)	⬆️
annif/backend/http.py	100% <100%> (ø)	⬆️
annif/backend/dummy.py	100% <100%> (ø)	⬆️
annif/backend/tfidf.py	100% <100%> (ø)	⬆️
annif/project.py	100% <100%> (ø)	⬆️
annif/backend/backend.py	90% <83.33%> (+2%)	⬆️
annif/eval.py	100% <0%> (+1.88%)	⬆️

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[coveralls]

Coverage increased (+0.3%) to 96.558% when pulling a2969d8 on backend-param into 4920996 on master.