Chi currently supports go down to 1.14, which has been EOL for almost 4 years.

This means keeping "code smells" around (e.g. ioutil) and blocking access to some newer features (e.g. ResponseController).

I propose bumping the minimal version to allow for more aggressive deprecations and feature adoption.

Concretely, I'd propose matching go's support policy of "latest+2", but would be happy with any other such dynamic approach, so that there's

1. a clearly defined expectation of support
2. no need to periodically rehash the support discussion

WDYT?