Add `Solar Alabama` dataset

[WenjieDu]

What does this PR do?

1. fixing #67;

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.
• [x] I have written necessary tests and already run them locally.

[coveralls]

Pull Request Test Coverage Report for Build 9680407770

Details

• 6 of 16 (37.5%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-1.2%) to 77.816%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tsdb/data_processing.py	1	2	50.0%
tsdb/loading_funcs/solar_alabama.py	4	13	30.77%
<!--	Total:	6	16	37.5%	-->

Totals
Change from base Build 9656339865:	-1.2%
Covered Lines:	449
Relevant Lines:	577

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9689623151

Details

• 16 of 16 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+4.4%) to 83.362%

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Totals
Change from base Build 9656339865:	4.4%
Covered Lines:	481
Relevant Lines:	577

---

💛 - Coveralls