Add plugin code

This adds basic plugins.
"main" types: veth, bridge, macvlan
"ipam" type: host-local

The code has been ported over from github.com/coreos/rkt project
and adapted to fit the CNI spec.

plugins/ipam/host-local/config.go

@@ -0,0 +1,57 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net"
+
+	"github.com/appc/cni/pkg/ip"
+	"github.com/appc/cni/pkg/plugin"
+)
+
+// IPAMConfig represents the IP related network configuration.
+type IPAMConfig struct {
+	Name       string
+	Type       string         `json:"type"`
+	RangeStart net.IP         `json:"rangeStart"`
+	RangeEnd   net.IP         `json:"rangeEnd"`
+	Subnet     ip.IPNet       `json:"subnet"`
+	Gateway    net.IP         `json:"gateway"`
+	Routes     []plugin.Route `json:"routes"`
+}
+
+type Net struct {
+	Name string      `json:"name"`
+	IPAM *IPAMConfig `json:"ipam"`
+}
+
+// NewIPAMConfig creates a NetworkConfig from the given network name.
+func LoadIPAMConfig(bytes []byte) (*IPAMConfig, error) {
+	n := Net{}
+	if err := json.Unmarshal(bytes, &n); err != nil {
+		return nil, err
+	}
+
+	if n.IPAM == nil {
+		return nil, fmt.Errorf("%q missing 'ipam' key")
+	}
+
+	// Copy net name into IPAM so not to drag Net struct around
+	n.IPAM.Name = n.Name
+
+	return n.IPAM, nil
+}