Eliminate useless chunking from TF-IDF backend. Fixes #85

[osma]

No description provided.

[codecov]

Codecov Report

Merging #91 into master will decrease coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #91      +/-   ##
=========================================
- Coverage   95.78%   95.7%   -0.08%     
=========================================
  Files          30      30              
  Lines        1234    1212      -22     
=========================================
- Hits         1182    1160      -22     
  Misses         52      52

Impacted Files	Coverage Δ
tests/test_backend_tfidf.py	100% <ø> (ø)	⬆️
tests/test_backend.py	100% <ø> (ø)	⬆️
annif/backend/tfidf.py	100% <100%> (ø)	⬆️

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[coveralls]

Coverage decreased (-0.08%) to 95.71% when pulling 5c6f28a on eliminate-chunking into cbb4c41 on master.

[coveralls]

Coverage decreased (-0.08%) to 95.71% when pulling 5c6f28a on eliminate-chunking into cbb4c41 on master.