Logging support

[acamargo]

Hello there, any chance to get logging support on it?

It could be like Typhoeus that when you declare a verbose: true option it set_debug_output($stdout) on net http request instance.

Even better, it could be a logger option where you inject your very own logger instance.

What do you think about it? I can make a pull request if this feature pleases you guys.

Thank you so much for this gem, btw. Awesome work.