Add documentation for Source 4 Explicit-Control and Continuations

[NhatMinh0208]

Description

This PR adds documentation for the Explicit-Control variant of Source 4, as well as the continuation functions.

Changes

• [X] add documentation for continuation functions in the form of continuation library
• [X] add specification for continuation library
• [X] add Source 4 Explicit-Control documentation
• [X] add Source 4 Explicit-Control specification

[coveralls]

Pull Request Test Coverage Report for Build 8457030586

Details

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 81.326%

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Totals
Change from base Build 8444837338:	0.002%
Covered Lines:	10629
Relevant Lines:	12671

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💛 - Coveralls