feat: Add #[ignore] macro

[skogseth]

Resolves #16.

After some discussion on #16 I went with the approach of accepting attributes following #[test] (for now only #[ignore] is accepted), as this would allow us to accept the standard syntax #[ignore = "some reason"] (and later #[should_panic = "some expected message"]). These are not allowed in custom attributes, but so long as we don't emit these (only parse them internally) it's all good.

[coveralls]

Pull Request Test Coverage Report for Build 18750725503

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 30.736%

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Totals
Change from base Build 18662789275:	0.3%
Covered Lines:	505
Relevant Lines:	1643

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💛 - Coveralls

[epage]

Looks good minus the test organization issue, thanks!

[epage]

Thanks!