Manual coverage-watermarks

[Ownezx]

In a similar way as desribed in https://llvm.org/docs/CommandGuide/llvm-cov.html, it would be interesting to be able to choose boundaries for the html report for the low/high colors to a different value than 80/100.

[taiki-e]

You can pass flags to llvm-cov via LLVM_COV_FLAGS environment variables, but I'm open to accept a PR to support this as CLI option of cargo-llvm-cov if it is needed.

https://github.com/taiki-e/cargo-llvm-cov#environment-variables

LLVM_COV_FLAGS -- A space-separated list of additional flags to pass to all llvm-cov invocations that cargo-llvm-cov performs. See LLVM documentation for available options.