Add --fail-uncovered-{lines,regions,functions} options

[taiki-e]

        --fail-uncovered-lines <MAX>
            Exit with a status of 1 if the uncovered lines are greater than MAX

        --fail-uncovered-regions <MAX>
            Exit with a status of 1 if the uncovered regions are greater than MAX

        --fail-uncovered-functions <MAX>
            Exit with a status of 1 if the uncovered functions are greater than MAX

There is no --fail-uncovered-branches option because branch coverage is not supported yet by rustc (#8).

Closes #170

[taiki-e]

cc @michaelvlach

[taiki-e]

bors r+

[bors]

Build succeeded:

• ci

[taiki-e]

Published in 0.4.4.