Update docs, add the func load(), and turn ucr&uea datasets' labels into float

[WenjieDu]

What does this PR do?

1. update README;
2. add load(), working the same as load_dataset();
3. fixing #39;

Before submitting

• [x] This PR is made to fix a typo or improve the docs (you can dismiss the other checks if this is the case).
• [x] Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• [x] I have commented my code, particularly in hard-to-understand areas.

[github-actions[bot]]

Pull Request Test Coverage Report for Build 6219042935

• 1 of 2 (50.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.08%) to 67.896%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tsdb/data_processing.py	1	2	50.0%
<!--	Total:	1	2	50.0%	-->

Totals
Change from base Build 6138443354:	-0.08%
Covered Lines:	313
Relevant Lines:	461

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💛 - Coveralls