Code restructuring, assigning proper subsystems to each

- Drivers contain
    * donut/*
    * file/*
    * memory/*

 - Storage format contains
    * donut/*
      - GetObject() --> renamed to GetObjectReader()
      - Deleted stale objectwriter.go, renamed donutwriter.go to object_writer.go

Simplifying, and documenting codebase further

pkg/drivers/file/file.go

@@ -0,0 +1,41 @@
+/*
+ * Minimalist Object Storage, (C) 2015 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 file
+
+import (
+	"os"
+	"sync"
+
+	"github.com/minio-io/minio/pkg/drivers"
+)
+
+// Start filesystem channel
+func Start(root string) (chan<- string, <-chan error, drivers.Driver) {
+	ctrlChannel := make(chan string)
+	errorChannel := make(chan error)
+	s := new(fileDriver)
+	s.root = root
+	s.lock = new(sync.Mutex)
+	go start(ctrlChannel, errorChannel, s)
+	return ctrlChannel, errorChannel, s
+}
+
+func start(ctrlChannel <-chan string, errorChannel chan<- error, s *fileDriver) {
+	err := os.MkdirAll(s.root, 0700)
+	errorChannel <- err
+	close(errorChannel)
+}