Add `page.driver.downloads` API?

[botandrose]

Heya, I've recently been migrating my projects from my own driver at https://github.com/botandrose/capybara-headless_chrome to this one. Much better! Thank you so very much!

However, there is one thing that I miss from my old driver: a nice downloads API. So, I've quickly extracted it and hooked it up to Cuprite via https://github.com/botandrose/cuprite-downloads . I'm opening this issue to ask if there's any interest in eventually merging something like this into Cuprite itself?

[route]

I like it! Why don't you open PR for Cuprite? :)