Config.__getattr__ should raise AttributeError

[hadrianl]

Description

Make __getattr__ to raise AttributeError instead of return it.Avoid using try except

Motivation and Context

User should be responsible for getting the wrong attribute.To return AttributeError might cause unexpected problems.Raise it instead.Also, aviod using try except syntax

How Has This Been Tested?

• Pass the test by running: pytest qlib/tests/test_all_pipeline.py under upper directory of qlib.
• If you are adding a new feature, test on your own test scripts.

Screenshots of Test Results (if appropriate):

1. Pipeline test:
2. Your own tests:

Types of changes

• [ x ] Fix bugs
• Add new feature
• Update documentation

[ghost]

All CLA requirements met.

[you-n-g]

@hadrianl
Many thanks for your contribution!

[hadrianl]

Excellent Project!keep up the good work!