Add event on HttpClient

[domthomas-dev]

Hi,
Before doing a PR, I want to know that you think about this.
I think it will be a good thing if events are raised when HttpClient makes a post request, a get request, etc.

With this we could add listeners, for example, Log, Control, check, etc.

Thanks

[domthomas-dev]

Have you got an example ? it allows me to start PR

I don't know if I must create an event class, or do like Eloquent event.