建议: 将所有与语法相关的元数据移动到 `grammars.yml`

Moreover, the difficulties related by @pastra98 made me realise there's more we could be doing with regards to locating grammar and license files. Specifically, we should be able to provide a manual path if need be — the currently hardcoded search locations can remain the default for grammars without a src: field defined, or whatever.