Remove console io

`io/console` is part of Ruby and coolline itself works without the gem. As
it turns out, this gem dependency is actually unnecessary and is
preventing pry-coolline from building under Ruby 2.0 (as the io-console
gem has native extensions that fail to configure). Remove the gem
dependency and instead use the `io/console` that already ships with Ruby
1.9.x to also support Ruby 2.0.0

Additionally, update the dependency on coolline to `~> 0.4.0`