Ignore ip range using regex

Implements feature to allow ignoring IP address ranges using a regex.  Use case for me was that I needed to ignore a large volume of IP addresses from a particular corporate network, maintaining a large list of IPs would be tedious and also potentially slow to iterate on every request.

Example:
```ruby
Split.configure do |c|
    c.ignore_ip_addresses << /81\.19\.48\.[0-9]+/
end
```