Create blob backed up by filesystem (#55)

* create a blob backed up by filesystem
* added code coverage test for filesystem blobs
* updated readme for using filesystem
* install peer dep
* added from to files array in package.json

package.json

@@ -4,6 +4,7 @@
     "description": "A Blob implementation in Node.js, originally from node-fetch.",
     "main": "index.js",
     "files": [
+        "from.js",
         "index.js",
         "index.d.ts"
     ],
@@ -48,5 +49,7 @@
             }
         ]
     },
-    "dependencies": {}
+    "peerDependencies": {
+        "domexception": "^2.0.1"
+    }
 }