Clean up examples/ directory

[mattdangerw]

There are a few minor cleanups we should do in the examples/ directory for the 0.4 release.

• We should remove the base readme https://github.com/keras-team/keras-nlp/blob/master/examples/README.md, it is quite out of date now that our models have moved inside the library.
• We should remove bert_glue_finetune.py. The new glue finetuning example is now much more fully featured.
• We should rename the bert example to reflect it is now about pretraining specifically. Something like renaming bert/ to bert_pretraining/, bert_train.py -> bert_pretrain.py, bert_preprocess.py -> bert_create_pretraining_data.py.

[chenmoneygithub]

I will handle this BERT pretraining later, it needs a few more works, e.g., using the MLMMaskGenerator to generate masks in our preprocessing.

[ADITYADAS1999]

There are a few minor cleanups we should do in the examples/ directory for the 0.4 release.

• We should remove the base readme https://github.com/keras-team/keras-nlp/blob/master/examples/README.md, it is quite out of date now that our models have moved inside the library.
• We should remove bert_glue_finetune.py. The new glue finetuning example is now much more fully featured.
• We should rename the bert example to reflect it is now about pretraining specifically. Something like renaming bert/ to bert_pretraining/, bert_train.py -> bert_pretrained.py, bert_preprocess.py -> bert_create_pretraining_data.py.

hey mattdangerw this issue is open for work? Can I go through this 😃

[chenmoneygithub]

@ADITYADAS1999 thank you! Contributions are definitely welcome for this issue!