Use `inherit` instead of carrying settings down manually

Need to test this more, but apparently this works in some places:

``` css
body {
font-feature-settings: "kern" 1, "smcp" 1;
}

p {
font-feature-settings: "smcp"; /* This acts like you wrote `"kern" 0;` which is annoying */
font-feature-settings: "smcp" 1, "smcp" 1; /* What I’m doing now */
font-feature-settings: "kern" inherit, "smcp" inherit; /* Verbose, but easier to maintain. */
}
```

No file or test is named. Start by reviewing the repository’s OpenType CSS declarations and checking the behavior of `font-feature-settings` inheritance in the issue’s examples; done means the supported settings are handled consistently without manual carry-down.

Written by the indexing model from the issue text.