Add additional option support

In RedHat there are many more options that can be specified after the interface. For example, you can specify a routing table such as `default via 10.0.0.1 dev eth1 table 200`. Everything after the interface is so fluid it doesn't make sense to add specific properties for everything. A simple `additional_options` property is most flexible.

I don't know what or if any additional options are available in Debian but I added support anyway. It certainly shouldn't hurt. If someone else can test the Debian side to see if it's needed that'd be great.

Please let me know if you have any questions.
I've got a few comments on how this property behaves.

First off, the network_config type uses `options` for setting arbitrary options, I would like to match that convention here for the sake of consistency. Would you be amenable to renaming this to `options`?

Secondly, right now only redhat and debian are supported but it's possible to add more route providers, and those may not necessarily support additional options. Could you pull out a feature for this property like the options property does for network_config 9https://github.com/adrienthebo/puppet-network/blob/master/lib/puppet/type/network_config.rb#L93)? 

Lastly, what sort of values should this be? Should it be a string, hash, or something else? Can we do some sort of validation to make sure we only set reasonable route options? And could you add some documentation of how this could be used and in what cases?