Epub support

[coveralls]

Pull Request Test Coverage Report for Build 48

• 96 of 112 (85.71%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+9.04%) to 86.165%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/core/core.go	82	98	83.67%
<!--	Total:	96	112	85.71%	-->

Totals
Change from base Build 42:	9.04%
Covered Lines:	355
Relevant Lines:	412

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💛 - Coveralls