Minor middleware improvements. No changes to core library/router. Moving v3 into its own branch as a version of chi for Go 1.7, 1.8, 1.9, 1.10, 1.11
History of changes: v3.3.3...v3.3.4
Master will switch into v4, where we will only support Go versions inline with Go's own policy, https://golang.org/doc/devel/release.html#policy (aka, last 2 versions)