It now decouples `env.params` to `env.params.query`, `env.params.body`,
`env.params.json` and `env.params.url` and you still can access merged
values using `env.params.all`
`301` means "Moved Permanently", so browser caches this redirect, it is used when changing server URL.
`302` means "Found", it is used generally (e.g. redirect top page after
login).
Each of `301`, `302`, `303` and `307` means redict, but they are
different. We could choice those status in case.
