Allow http request read/open timeout to be set.

Should fix errors like this:

```
A Faraday::Error::ConnectionFailed occurred in controller#index:

  end of file reached
  /usr/local/lib/ruby/1.9.1/openssl/buffering.rb:145:in `sysread_nonblock'
```

by doing this:

```ruby
Restforce.configure do |config|
  config.timeout = 100
end
```