Automatic histogram size selection

[RoelBouman]

This PR adds new functionality to PyOD by allowing for automatic determination of the optimal number of bins for histograms. This can therefore improve the results from HBOS and LODA.

The PR solves #189

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• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
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All Submissions Cores:

• Have you added an explanation of what your changes do and why you'd like us to include them?
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• Does your submission have appropriate code coverage? The cutoff threshold is 95% by Coversall.

[coveralls]

Pull Request Test Coverage Report for Build 2065

• 194 of 196 (98.98%) changed or added relevant lines in 6 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.1%) to 95.923%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyod/models/loda.py	42	44	95.45%

Files with Coverage Reduction	New Missed Lines	%
pyod/models/cof.py	1	98.59%
pyod/test/test_cof.py	1	99.4%

Totals
Change from base Build 2052:	0.1%
Covered Lines:	5599
Relevant Lines:	5837

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 2057

• 173 of 196 (88.27%) changed or added relevant lines in 6 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.3%) to 95.506%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyod/models/loda.py	21	44	47.73%

Totals
Change from base Build 2052:	-0.3%
Covered Lines:	5483
Relevant Lines:	5741

---

💛 - Coveralls

[RoelBouman]

Due to the fail of the coveralls check I noted a mistake in one of the newer tests I've written. This should now be fixed.
In addition, I've updated HBOS and LODA documentation in this PR to be in line with ABOD and COF.

[yzhao062]

This looks great. I will take care of other formatting and documentation thing. Thanks a lot and sorry for being late.