Bilou on refactored iob

[Kebniss]

To do:

• [x] Make Wapiti BILOU compatible
• [x] Add test for Wapiti with Bilou on
• [x] Add test for wapiti.merge_top_n
• [x] Add tests for grouping.py
• [x] Add BILOU detokenize tests

[codecov[bot]]

Codecov Report

Merging #65 into master will increase coverage by 7.78%. The diff coverage is 97.68%.

@@            Coverage Diff            @@
##           master     #65      +/-   ##
=========================================
+ Coverage   81.02%   88.8%   +7.78%     
=========================================
  Files          40      42       +2     
  Lines        2092    2341     +249     
=========================================
+ Hits         1695    2079     +384     
+ Misses        397     262     -135

[Kebniss]

Both the use of X_dev and y_dev when fitting and the specification of a model filename are not currently working in wapiti. These issues are linked to how wapiti pipeline is built. They need further analysis and I will address them in a separate PR

[Kebniss]

Tests run fine on my laptop, I think there is an issue with Wapiti installation in travis