config/main: Re-write config files - add to new config v3

- New config format.

```
{
	"version": "3",
	"address": ":9000",
    "backend": {
          "type": "fs",
          "disk": "/path"
    },
	"credential": {
		"accessKey": "WLGDGYAQYIGI833EV05A",
		"secretKey": "BYvgJM101sHngl2uzjXS/OBF/aMxAN06JrJ3qJlF"
	},
	"region": "us-east-1",
	"logger": {
		"file": {
			"enable": false,
			"fileName": "",
			"level": "error"
		},
		"syslog": {
			"enable": false,
			"address": "",
			"level": "debug"
		},
		"console": {
			"enable": true,
			"level": "fatal"
		}
	}
}
```

New command lines in lieu of supporting XL.

Minio initialize filesystem backend.
~~~
$ minio init fs <path>
~~~

Minio initialize XL backend.
~~~
$ minio init xl <url1>...<url16>
~~~

For 'fs' backend it starts the server.
~~~
$ minio server
~~~

For 'xl' backend it waits for servers to join.
~~~
$ minio server
... [PROGRESS BAR] of servers connecting
~~~

Now on other servers execute 'join' and they connect.
~~~
....
minio join <url1> -- from <url2> && minio server
minio join <url1> -- from <url3> && minio server
...
...
minio join <url1> -- from <url16> && minio server
~~~

access-key.go

@@ -0,0 +1,96 @@
+/*
+ * Minio Cloud Storage, (C) 2015, 2016 Minio, 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 (
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"regexp"
+
+	"github.com/minio/minio/pkg/probe"
+)
+
+// credential container for access and secret keys.
+type credential struct {
+	AccessKeyID     string `json:"accessKey"`
+	SecretAccessKey string `json:"secretKey"`
+}
+
+// stringer colorized access keys.
+func (a credential) String() string {
+	accessStr := colorMagenta("AccessKey: ") + colorWhite(a.AccessKeyID)
+	secretStr := colorMagenta("SecretKey: ") + colorWhite(a.SecretAccessKey)
+	return fmt.Sprint(accessStr + "  " + secretStr)
+}
+
+const (
+	minioAccessID = 20
+	minioSecretID = 40
+)
+
+// isValidSecretKey - validate secret key.
+var isValidSecretKey = regexp.MustCompile("^.{40}$")
+
+// isValidAccessKey - validate access key.
+var isValidAccessKey = regexp.MustCompile("^[A-Z0-9\\-\\.\\_\\~]{20}$")
+
+// mustGenAccessKeys - must generate access credentials.
+func mustGenAccessKeys() (creds credential) {
+	creds, err := genAccessKeys()
+	fatalIf(err.Trace(), "Unable to generate access keys.", nil)
+	return creds
+}
+
+// genAccessKeys - generate access credentials.
+func genAccessKeys() (credential, *probe.Error) {
+	accessKeyID, err := genAccessKeyID()
+	if err != nil {
+		return credential{}, err.Trace()
+	}
+	secretAccessKey, err := genSecretAccessKey()
+	if err != nil {
+		return credential{}, err.Trace()
+	}
+	creds := credential{
+		AccessKeyID:     string(accessKeyID),
+		SecretAccessKey: string(secretAccessKey),
+	}
+	return creds, nil
+}
+
+// genAccessKeyID - generate random alpha numeric value using only uppercase characters
+// takes input as size in integer
+func genAccessKeyID() ([]byte, *probe.Error) {
+	alpha := make([]byte, minioAccessID)
+	if _, e := rand.Read(alpha); e != nil {
+		return nil, probe.NewError(e)
+	}
+	for i := 0; i < minioAccessID; i++ {
+		alpha[i] = alphaNumericTable[alpha[i]%byte(len(alphaNumericTable))]
+	}
+	return alpha, nil
+}
+
+// genSecretAccessKey - generate random base64 numeric value from a random seed.
+func genSecretAccessKey() ([]byte, *probe.Error) {
+	rb := make([]byte, minioSecretID)
+	if _, e := rand.Read(rb); e != nil {
+		return nil, probe.NewError(e)
+	}
+	return []byte(base64.StdEncoding.EncodeToString(rb))[:minioSecretID], nil
+}