* Preserve spaces in GPT-2 tokenizers
Preserves spaces after special tokens in GPT-2 and inhereted (RoBERTa)
tokenizers, enabling correct BPE encoding. Automatically inserts a space
in front of first token in encode function when adding special tokens.
* Add tokenization preprocessing method
* Add framework argument to pipeline factory
Also fixes pipeline test issue. Each test input now treated as a
distinct sequence.
This construct isn't used anymore these days.
Running python tests/test_foo.py puts the tests/ directory on
PYTHONPATH, which isn't representative of how we run tests.
Use python -m unittest tests/test_foo.py instead.
