Support http.route tag (and span naming) if possible

[codefromthecrypt]

The "http.route" tag indicates a route expression like /users/:userId that corresponded with an http request. I'm not sure the aio framework has routing language or not, but if so, it will be nice.

https://zipkin.io/public/thrift/v1/zipkinCore.html#Const_HTTP_ROUTE

Note: the naming expression you use is the same as Brave, except it now uses templates and keywords for redirect or not found

openzipkin/brave#602

[jettify]

There is language for routine like:
/foo/bar/{name}
foo/bar/
r/foo/bar/{name:\d+}
I just have not found good API to retrieve it, may be I missed something.

[jettify]

@asvetlov can you point me into right direction? For now I do not see better way than request.match_info.route.get_info()['formatter'])

[jettify]

As discussed special route should appear in aiohttp first aio-libs/aiohttp#2968