Enable `Parser`-based `ParserIterator` to work

[cky]

Now that we have associated types for Parser (#1626), we can finally make ParserIterator support any Parser, not just FnMut(I) -> IResult<I, O, E>.

[coveralls]

Pull Request Test Coverage Report for Build 4051768316

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.5%) to 62.75%

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Files with Coverage Reduction	New Missed Lines	%
src/character/complete.rs	1	81.82%
src/character/streaming.rs	1	78.38%
<!--	Total:	2		-->

Totals
Change from base Build 3981619336:	0.5%
Covered Lines:	1570
Relevant Lines:	2502

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💛 - Coveralls