Add ability to load all text files from a subdirectory for training (#1997)

* Update utils.py

returns individual txt files and subdirectories to getdatasets to allow for training from a directory of text files

* Update training.py

minor tweak to training on raw datasets to detect if a directory is selected, and if so, to load in all the txt files in that directory for training

* Update put-trainer-datasets-here.txt

document

* Minor change

* Use pathlib, sort by natural keys

* Space

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Co-authored-by: oobabooga <112222186+oobabooga@users.noreply.github.com>

training/datasets/put-trainer-datasets-here.txt

@@ -0,0 +1 @@
+to load multiple raw text files create a subdirectory and put them all there