Better API to adjust the default Apache `HttpClient` in google-http-client-apache 2.0.0?

[chanseokoh]

(From #576 (comment))

I need to create an HttpClient instance that is slightly different from the default HttpClient created from newDefaultHttpClient(). I do need to set a lot of things in common with the default HttpClient; the most important one is .useSystemProperties(), but I'd like to have other things in sync with what newDefaultHttpClient() does too. The only way I can do now with the current API is to create an HttpClient instance from scratch with the Apache API, by duplicating the almost all code from newDefaultHttpClient(). Not only bad is the code duplication of the internal details, but the internal details of newDefaultHttpClient() can change with new releases.

How about providing newDefaultHttpClientBuilder() API?