Add POS tagging and Phrase chunking token classification examples (#6457)

* Add more token classification examples

* POS tagging example

* Phrase chunking example

* PR review fixes

* Add conllu to third party list (used in token classification examples)

examples/token-classification/run_pos_pl.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+if ! [ -f ./dev.txt ]; then
+  echo "Download dev dataset...."
+  curl -L -o ./dev.txt 'https://github.com/UniversalDependencies/UD_English-EWT/raw/master/en_ewt-ud-dev.conllu'
+fi
+
+if ! [ -f ./test.txt ]; then
+  echo "Download test dataset...."
+  curl -L -o ./test.txt 'https://github.com/UniversalDependencies/UD_English-EWT/raw/master/en_ewt-ud-test.conllu'
+fi
+
+if ! [ -f ./train.txt ]; then
+  echo "Download train dataset...."
+  curl -L -o ./train.txt 'https://github.com/UniversalDependencies/UD_English-EWT/raw/master/en_ewt-ud-train.conllu'
+fi
+
+export MAX_LENGTH=200
+export BERT_MODEL=bert-base-uncased
+export OUTPUT_DIR=postagger-model
+export BATCH_SIZE=32
+export NUM_EPOCHS=3
+export SAVE_STEPS=750
+export SEED=1
+
+
+# Add parent directory to python path to access lightning_base.py
+export PYTHONPATH="../":"${PYTHONPATH}"
+
+python3 run_pl_ner.py --data_dir ./ \
+--task_type POS \
+--model_name_or_path $BERT_MODEL \
+--output_dir $OUTPUT_DIR \
+--max_seq_length  $MAX_LENGTH \
+--num_train_epochs $NUM_EPOCHS \
+--train_batch_size $BATCH_SIZE \
+--seed $SEED \
+--gpus 1 \
+--do_train \
+--do_predict