Linear Metrics & More

[donglihe-hub]

What does this PR do?

1. automatically detect classification task type.
2. warn users when they attempt to measure p@k where I. k > 1 and task type is not multilabel. In such case, a fallback metric will be used, i.e., k@1; and II. k > number of classes. In such case a fallback metric will be used, i.e., k@num_classes. (nn does this while linear not)
3. support parallel training for linear techniques (currently only "1vsrest").
4. support "micro" and "macro" for linear Precision.

Test CLI & API (bash tests/autotest.sh)

Test APIs used by main.py.

• [ ] Test Pass
  • (Copy and paste the last outputted line here.)
• [ ] Not Applicable (i.e., the PR does not include API changes.)

Check API Document

If any new APIs are added, please check if the description of the APIs is added to API document.

• [ ] API document is updated (linear, nn)
• [ ] Not Applicable (i.e., the PR does not include API changes.)

Test quickstart & API (bash tests/docs/test_changed_document.sh)

If any APIs in quickstarts or tutorials are modified, please run this test to check if the current examples can run correctly after the modified APIs are released.