Add torch quickthought bert pretraining

[leezu]

Add an initial version of the torch pretraining scripts

cc @dmlc/gluon-nlp-team

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1540/5b2f7f120b419df1000d577ee89d4018d020a6a0/index.html

[codecov[bot]]

Codecov Report

Merging #1540 (6389487) into master (8e41885) will decrease coverage by 0.75%. The diff coverage is 21.42%.

@@            Coverage Diff             @@
##           master    #1540      +/-   ##
==========================================
- Coverage   83.77%   83.01%   -0.76%     
==========================================
  Files          62       62              
  Lines        8277     8191      -86     
==========================================
- Hits         6934     6800     -134     
- Misses       1343     1391      +48     

Impacted Files	Coverage Δ
setup.py	0.00% <0.00%> (ø)
src/gluonnlp/torch/models/bert.py	85.87% <25.00%> (-9.70%)	:arrow_down:
src/gluonnlp/torch/__init__.py	100.00% <100.00%> (ø)
src/gluonnlp/utils/__init__.py	100.00% <100.00%> (ø)
conftest.py	76.31% <0.00%> (-9.94%)	:arrow_down:
src/gluonnlp/data/loading.py	76.55% <0.00%> (-2.28%)	:arrow_down:
src/gluonnlp/utils/lazy_imports.py	58.42% <0.00%> (-2.25%)	:arrow_down:
src/gluonnlp/data/tokenizers/yttm.py	81.73% <0.00%> (-1.02%)	:arrow_down:
src/gluonnlp/torch/models/transformer.py	27.23% <0.00%> (-0.92%)	:arrow_down:
src/gluonnlp/data/tokenizers/spacy.py	65.33% <0.00%> (-0.91%)	:arrow_down:
... and 24 more

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[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1540/63894871c91d47fb122efbc6ba6c334ee54e970f/index.html