func ParamsFromContext(ctx context.Context) Params {
	p, _ := ctx.Value(ParamsKey).(Params)
	return p
}
ParamsFromContext pulls the URL parameters from a request context,
or returns nil if none are present.

This is only present from go 1.7.
package httprouter
import (
	"context"
	"net/http"
)
type paramsKey struct{}
var ParamsKey = paramsKey{}
func (r *Router) Handler(method, path string, handler http.Handler) {
	r.Handle(method, path,
		func(w http.ResponseWriter, req *http.Request, p Params) {
			ctx := req.Context()
			ctx = context.WithValue(ctx, ParamsKey, p)
			req = req.WithContext(ctx)
			handler.ServeHTTP(w, req)
		},
	)
}