feat(driver): expose Ferrum console as Driver#console - #351

Closes #113.

page.driver.console is Ferrum's Console for the current page: console.* calls, browser log entries and uncaught exceptions. It's Enumerable over the last 1000 messages and is cleared on reset, since every test gets a fresh page.

Until now the only way to see what the page logged was to pass a :logger and filter CDP frames out of its output. With Ferrum 0.20 that output also carries Chrome's own stderr, so those filters let browser noise through. rails_admin's ConsoleLogger is one example.

after { expect(page.driver.console.select(&:error?)).to be_empty }
after { page.driver.console.each { |message| warn(message) } }

Includes the ferrum ~> 0.20.0 bump the console API needs.