Enable features Optional features

[sridmad]

The Windows port does not port some of the features that are not core to Envoy. This issue is to track porting these optional features to Windows.

[IanDuncanson]

@sridmad - will this port include things such as the http extension filters? We are looking at how to enable grpc-web on windows, and are interested in the in-built filter in envoy - see the following discussion - grpc/grpc-web#189 (comment)