v3.1.0 release

Update README with latest benchmarks of v3

Update README, CHANGELOG, other comments

Release v2.0.0 with support for go1.8, http2 and http.Pusher

Import ordering for travis

Ensure we dont route to an empty mux, fixes go-chi#42

Merge pull request go-chi#33 from pressly/zeroalloc

Reuse root context in a sync pool to reduce GC: zero-alloc routing