Enable merge mode “replace” in include statements Previously only the merge modes “override” and “augment” were available in include statements, using the prefix ‘+’ and ‘|’ respectively. While on one hand `replace` include statement can be used in keymap files, on the other hand *rules* files have no way to express the *replace* mode. This commit enables the merge mode “replace” using the prefix `^`. This prefix was chosen due to its similarity with the `XOR` bit operator, which convey *mutual exclusion*. Other candidates: - `!` conveys some kind of higher precedence, akin to CSS `!important`. But it conflicts with the section header `!`, which is a token in the current parser. It would require special handling, not worth it. It also convey the meaning of negation, which is confusing. - `&` has the advantage of not corresponding to a token in the rules parser. `^` seems however to stand out more and it is less likely to trigger erroneous comparison with `|` and `&` bit operators.