router: add initial API client

[mweibel]

No description provided.

[disperate]

As there will be a interface API at some point in the not so far future, is going for RouterInterface the right direction? I assumed we would use a generic Interface Type.

[mweibel]

I initially wanted to use interface but we have already an interface type (and, accordingly, an Address type):

cloudscale-go-sdk/servers.go

Lines 68 to 81 in b10972e

	type Interface struct {
	Type string `json:"type,omitempty"`
	Network NetworkStub `json:"network,omitempty"`
	Addresses []Address `json:"addresses,omitempty"`
	}
	type Address struct {
	Version int `json:"version"`
	Address string `json:"address"`
	PrefixLength int `json:"prefix_length"`
	Gateway string `json:"gateway"`
	ReversePtr string `json:"reverse_ptr"`
	Subnet SubnetStub `json:"subnet"`
	}

The question I guess is, what do we do. We can e.g. rename the existing Interface to ServerInterface or LegacyInterface because we plan to unify them, and we'll need a new major version anyway due to #91, or we find another name.
Your opinon?

[disperate]

As discussed, keep RouterInterface as submitted. On the server, rename the Interface to ServerInterface. This will be a breaking change, but it keeps the naming consistent.

[mweibel]

done.