Unwrap "ocrx_line" as well as "ocr_line" as Fonduer has no data model

[HiromuHota]

Description of the problems or issues

Is your pull request related to a problem? Please describe.

Currently, parser unwraps "ocr_line" as Fonduer has no data model for lines.
However, hOCR could contains "ocrx_line" for lines.
Fonduer should unwrap this element as well for the same reason.

Does your pull request fix any issue.

N/A

Description of the proposed changes

Unwrap "ocrx_line" as well as "ocr_line" as Fonduer has no data model

Test plan

Use pdftotree (HazyResearch/pdftotree#95) to convert md.pdf to md.hocr, which contains "ocrx_line" elements.
And check if md.hocr can be correctly parsed.

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.

[HiromuHota]

The mypy complains:

src/fonduer/utils/utils_table.py:27: error: Value of type variable "_LT" of "min" cannot be "_T"
src/fonduer/utils/utils_table.py:29: error: Value of type variable "_LT" of "min" cannot be "_T"

This python/mypy#9582 could be related.

I will pin mypy at 0.782 for now and address it in a different issue.

[codecov-io]

Codecov Report

Merging #526 into master will decrease coverage by 0.00%.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master     #526      +/-   ##
==========================================
- Coverage   86.03%   86.02%   -0.01%     
==========================================
  Files          92       92              
  Lines        4769     4774       +5     
  Branches      896      899       +3     
==========================================
+ Hits         4103     4107       +4     
- Misses        475      476       +1     
  Partials      191      191              

Flag	Coverage Δ
#unittests	86.02% <57.14%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
...duer/parser/preprocessors/hocr_doc_preprocessor.py	86.31% <57.14%> (-0.36%)	⬇️