Skip autogenerated code in code coverage

[zbraniecki]

This is not yet ready to merge. I'm experimenting with ways to skip codegen code in codecoverage.

[coveralls]

Pull Request Test Coverage Report for Build 39

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 28.734%

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Totals
Change from base Build 38:	0.0%
Covered Lines:	504
Relevant Lines:	1754

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💛 - Coveralls

[zbraniecki]

This is now ready for review. This change makes the generated code be skipped by codecoverage (at least most of it - skipping whole modules is not yet supported - https://github.com/xd009642/tarpaulin/issues/138 )

[zbraniecki]

This raises our total codecoverage to 89% - https://coveralls.io/github/unclenachoduh/pluralrules