Windows Support

Patch for https://github.com/containernetworking/plugins/pull/85

+ Windows cni plugins are added
   (*) win-bridge (hostgw)
   (*) win-overlay (vxlan)
+ Windows netconf unit test
+ Fix appveyor config to run the test
+ Build release support for windows plugins

Address comments

From:
    - https://github.com/containernetworking/plugins/pull/85
    - 0049c64e3f

README.md

@@ -14,7 +14,9 @@ Read [CONTRIBUTING](CONTRIBUTING.md) for build and test instructions.
 * `macvlan`: Creates a new MAC address, forwards all traffic to that to the container.
 * `ptp`: Creates a veth pair.
 * `vlan`: Allocates a vlan device.
-
+#### Windows: windows specific
+* `win-bridge`: Creates a bridge, adds the host and the container to it.
+* `win-overlay`: Creates an overlay interface to the container.
 ### IPAM: IP address allocation
 * `dhcp`: Runs a daemon on the host to make DHCP requests on behalf of the container
 * `host-local`: maintains a local database of allocated IPs