[v2] Return error from cursor encoder & decoder

[pilagod]

Return error from cursor encoder & decoder, also propagating error to paginator.

[coveralls]

Pull Request Test Coverage Report for Build 98

• 100 of 112 (89.29%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.7%) to 94.643%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
paginator/paginator.go	22	34	64.71%
<!--	Total:	100	112	89.29%	-->

Totals
Change from base Build 91:	-0.7%
Covered Lines:	212
Relevant Lines:	224

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💛 - Coveralls