Http client API

[Kurchi Subhra Hazra]

>> - HttpClient createClient() -- is this the same as 
>> HttpClientProvider.provider().createAsynchronousHttpClient()?
> yes, and that needs to be documented.
Just on this one, the method name createAsynchronousHttpClient() looks 
like a remnant of our previous API iterations, and I think this
should just be renamed to createHttpClient() or createClient().

- Kurchi