WIP: symfony v4 + 7.1 bump

[dbu]

awesome to see this :+1:

if you get stuck, ping me and i will try to help find whats wrong.

[lunetics]

First i'm gonna just do chores like return types / php 7 compat etc. Other goal would be to split the "real" logic into a dedicated pure package (lunetics/locale) which does the locale detection etc and keep this as sole integration bundle of this lib

[goetas]

done in 3.x