use built-in 'warnings' lib for handling warning/error messages
The built-in warnings lib provides a flexible way to handle warnings and error messages, including making it easy to set which warnings will throw exceptions, which ones will print, etc. This comes out of a discussion with @mvdan:
_hc: the "unknown metadata" error should just be a warning, since this will be a long term release
_hc: I can do that in the packaging
_hc: or we can figure out how to handle it in git
mvdan: hm
mvdan: not sure I agree entirely
mvdan: what about garbage? like adlkfjasf:bar
_hc: there is a warning for that
mvdan: sure it'll be a warning, but those are an error right now in fdroiddata CI
mvdan: which is useful
mvdan: warnings will go unnoticed
_hc: I don't know of a way to tell garbage from new tag
mvdan: on CI, I mean
_hc: there needs to be something like gcc's -Werror
_hc: make warnings errors
mvdan: okay
mvdan: and then we can use it in CI