You clone the repository, checkout the janino_scripting branch and build the jar file e.g. via mvn clean install.
Please note that the syntax of this new feature has further evolved and is described in the initial comment of this pull request. E.g. speed_factor and max_speed was merged and instead of first_match there are now statements with if, else and else if.
btw: the map matching service is now already included in the same repository so no more hassle like you had in Recent Core Build Fails
btw2: currently map matching does not support custom profiles per-request - only if defined on the server-side, but I guess this is sufficient for your needs as this was always the case.