Would be cool to be able to for example invert a filter like `!whatever` And could be useful with custom fields (https://github.com/zgoat/goatcounter/issues/191) e.g. ``` https://test.goatcounter.com/count?p=/hello&nojs=true ``` then be able to filter `nojs=true` and `!nojs=true` 😉 What do you think?
