Additional coverage measurements

[cgewecke]

Tracking/reference issue for additional coverage measurements that

• can be added in 0.7.0
• we have a plausible way of implementing

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• Public storage variable line coverage (Instrument public storage variable getters #281) (design idea)
• Modifier-hits-at-call-site branch coverage (Improve modifer coverage report #286) (design idea
• && / || Coberatura-style branch coverage (Accuracy for && and || #175) (design idea)
• Restore ternary conditional branch coverage (Reimplement ternary instrumentation #219) (design idea)
• Documentation coverage (investigate viability at solidity-parser-antlr)