Add multiline Japanese strings support to HocrVisualParser() to fix #534 and redo #537

[YasushiMiyata]

Description of the problems or issues

Is your pull request related to a problem? Please describe.
See #534.
This request redoes #537, which needs prior fixing #538 (fixed by #539).

Does your pull request fix any issue.
See #534

Description of the proposed changes

In case of multi line Japanese strings 'AAAA\nBBBB', spacy[ja] sometimes generates tokens ['AAA', 'AB', 'B', 'BB']. Proposal defines bbox of 'AB' as a multi line word (i.e. left is min left of ['A','B'], top is the top of 'A', right is max right of ['A','B'] and bottom is the bottom of 'B').

Test plan

This is cause of Japanese morphological analysis. So, I have added Japanese test data to 'tests/data/hocr_simple/japan.hocr' and test code to 'tests/parser/test_parser.py::test_parse_hocr'

Checklist

• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated the CHANGELOG.rst accordingly.

[codecov-commenter]

Codecov Report

Merging #542 (d76bd76) into master (5ab8e9c) will increase coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head d76bd76 differs from pull request most recent head 5ca10e8. Consider uploading reports for the commit 5ca10e8 to get more accurate results

@@            Coverage Diff             @@
##           master     #542      +/-   ##
==========================================
+ Coverage   86.02%   86.07%   +0.04%     
==========================================
  Files          92       92              
  Lines        4773     4775       +2     
  Branches      899      899              
==========================================
+ Hits         4106     4110       +4     
+ Misses        476      475       -1     
+ Partials      191      190       -1     

Flag	Coverage Δ
unittests	86.07% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...fonduer/parser/visual_parser/hocr_visual_parser.py	97.64% <100.00%> (+2.46%)	⬆️

[lukehsiao]

To avoid the need for you to rebase this again, I'm going to squash these commits and merge. But please update your other PR to be based off master if possible.