The SCSS that styles the `literal`, `code`, `file`, and `command` roles
is excessively complex because the traduction from RST to HTML is not
consistent from one role to another: some use `<code>` elements, some
have the `code` class, some wrap the literal with a `span` element.
This commit sets the `o_code` class on all of these roles' parent node
at translation time to allow simplifying the SCSS target.
fe7bc47fea