Improve question answering accessibility

[saeub]

• Fix tests
• Add test for font size configuration
• Update documentation

[codecov]

Codecov Report

Merging #27 (7f9fd25) into dev (88ee882) will increase coverage by 0.26%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev      #27      +/-   ##
==========================================
+ Coverage   65.76%   66.02%   +0.26%     
==========================================
  Files          21       21              
  Lines        2074     2090      +16     
==========================================
+ Hits         1364     1380      +16     
  Misses        710      710              

Impacted Files	Coverage Δ
lib/src/tasks/question_answering.dart	98.73% <100.00%> (+0.06%)	⬆️

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