add go 1.12 to ci

middleware: fix Compress to return passed down status code

release v4.0.0

update README, and add go.mod to _examples

Changelog: Implications of Go modules: Go 1.10.3+ & new import path

tiny fix: formatting of previous PR

Remove go.mod, stick to +incompatible versions for v3.x (go-chi#346)

Release v3.3.1

Release v3.3.0