Update status of ATS and OpenResty host implementations. (#49)

While there, drop link to Istio Proxy, since it's no different
than other Envoy implementations.

Signed-off-by: Piotr Sikora <[email protected]>

Author: PiotrSikora

README.md

@@ -28,18 +28,16 @@ Proxy-Wasm extensions across different proxies.
 
 #### Servers
 
+* [ATS]
 * [Envoy]
-* [Istio Proxy] (Envoy-based)
 * [NGINX]
 * [MOSN]
-* [ATS] (work-in-progress)
-* [OpenResty] (work-in-progress)
+* [OpenResty]
 
+[ATS]: https://docs.trafficserver.apache.org/en/latest/admin-guide/plugins/wasm.en.html
 [Envoy]: https://github.com/envoyproxy/envoy
-[Istio Proxy]: https://github.com/istio/proxy
 [NGINX]: https://github.com/Kong/ngx_wasm_module
 [MOSN]: https://github.com/mosn/mosn
-[ATS]: https://docs.trafficserver.apache.org/en/latest/admin-guide/plugins/wasm.en.html
 [OpenResty]: https://github.com/api7/wasm-nginx-module
 
 #### Libraries