introduced new outer bounds, unit cube-ellipsoid mixtures

[coveralls]

Pull Request Test Coverage Report for Build 4469354892

• 460 of 463 (99.35%) changed or added relevant lines in 6 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 97.692%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
nautilus/sampler.py	3	4	75.0%
nautilus/bounds/union.py	128	130	98.46%
<!--	Total:	460	463	99.35%	-->

Totals
Change from base Build 4418732783:	0.1%
Covered Lines:	1016
Relevant Lines:	1040

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💛 - Coveralls