Use custom HttpConnector when authentication

[ohtake]

I'm trying to modify ghprb-plugin so that it can work behind authentication proxies.
I added a HttpConnector implementation to ghprb-plugin:

public class HttpConnectorWithJenkinsProxy implements HttpConnector{
    public HttpURLConnection connect(URL url) throws IOException {
        return (HttpURLConnection)ProxyConfiguration.open(url);
    }
}

Since all GitHub constructors are private, there is no way to call #setConnector before GitHub(String, String, Sttring, String) constructor calls #getMyself, nor to extend GitHub class.
So I added HttpConnector parameter to connect* methods, except connectToEnterprise which does not require proxies in most cases.

[buildhive]

Kohsuke Kawaguchi » github-api #221 SUCCESS
This pull request looks good
(what's this?)

[ohtake]

A lot of overloads of connect* are hard to use.
I think it is better to introduce a builder class.

public class GitHubBuilder {
    public GitHubBuilder() {}

    public static GitHubBuilder fromPropertyFile() {}

    public GitHubBuilder withEndpoint(String endpoint) {}
    public GitHubBuilder withPassword(String user, String password) {}
    public GitHubBuilder withOAuthToken(String token) {}
    public GitHubBuilder withHttpConnector(HttpConnector connector) {}

    public GitHub build() {}
}

I close this pull request and will create another one tomorrow.