XL: Rename, cleanup and add more comments. (#1769)

- xl-v1-bucket.go - removes a whole bunch of code.
- {xl-v1,fs-v1}-metadata.go - add a lot of comments and rename functions
   appropriately.

docs/backend/fs/format.json

@@ -0,0 +1,4 @@
+{
+  "format": "fs",
+  "version": "1"
+}

docs/backend/fs/fs.json

@@ -0,0 +1,15 @@
+{
+    "version": "1",
+    "format": "fs",
+    "minio": {
+        "release": "DEVELOPMENT.GOGET"
+    },
+    "parts": [
+        {
+            "number": 1,
+            "name": "object1",
+            "size": 29,
+            "eTag": "",
+        },
+    ]
+}

docs/backend/fs/uploads.json

@@ -0,0 +1,10 @@
+{
+    "version": "1",
+    "format": "fs",
+    "uploadIds": [
+        {
+            "uploadID": "id",
+            "startTime": "time",
+        }
+    ]
+}