Implement Virtual DNS endpoints

[Tenzer]

https://api.cloudflare.com/#virtual-dns-users-
https://api.cloudflare.com/#virtual-dns-organizations-

[elithrar]

I'd like to split Virtual DNS out into its own sub-package: we currently only implement one endpoint on the User, but not the Org.

e.g.

import (
     "github.com/cloudflare/cloudflare-go"
     "github.com/cloudflare/cloudflare-go/virtualdns"
)

    ...
    client, err := cloudflare.New(key, email)
    ...
    vdns, err := virtualdns.NewClient(client)
    ...
    vdns.SetOrg(orgID) // Optional; causes us to use the /organizations/:id endpoint format.

    vdns.GetClusters()
    vdns.CreateClusters()
    // etc.

Objections? Proposing a similar approach for non-zone related services.

[elithrar]

WIP: #109

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.