Separate Mappable from ImmutableMappable

To each one of them implement one way of `init?(fromFileName file: String)`.

JSONStub.podspec

@@ -8,7 +8,7 @@
 
 Pod::Spec.new do |s|
   s.name             = 'JSONStub'
-  s.version          = '0.1.2'
+  s.version          = '0.1.3'
   s.summary          = 'Use JSONStub to easily load JSON files into your Mappable objects.'
 
 # This description is used to generate tags and improve search results.

JSONStub/Classes/BaseMappable.swift

@@ -10,16 +10,6 @@ import struct Foundation.Data
 import protocol ObjectMapper.BaseMappable
 
 public extension BaseMappable {
-    init?(fromFileName file: String) {
-        guard let json = file.fileDictionary() else { return nil }
-
-        self.init(JSON: json)
-    }
-
-    init?(fromStub stub: FileStub) {
-        self.init(fromFileName: stub.fileName)
-    }
-
     var asData: Data {
         guard let json = toJSONString(), let data = json.data(using: .utf8), json != "{}" else { return Data() }
 

JSONStub/Classes/ImmutableMappable.swift

@@ -9,11 +9,15 @@
 import protocol ObjectMapper.ImmutableMappable
 
 public extension ImmutableMappable {
-    init?(fromFileName file: String) {
+    init?(fromFileName file: String) throws {
         guard let json = file.fileDictionary() else { return nil }
 
+        try self.init(JSON: json)
+    }
+
+    init?(fromStub stub: FileStub) {
         do {
-            try self.init(JSON: json)
+            try self.init(fromFileName: stub.fileName)
         } catch {
             return nil
         }

JSONStub/Classes/Mappable.swift

@@ -0,0 +1,21 @@
+//
+//  Mappable.swift
+//  Pods
+//
+//  Created by Rafael Ferreira on 3/30/17.
+//
+//
+
+import protocol ObjectMapper.Mappable
+
+extension Mappable {
+    init?(fromFileName file: String) {
+        guard let json = file.fileDictionary() else { return nil }
+
+        self.init(JSON: json)
+    }
+
+    init?(fromStub stub: FileStub) {
+        self.init(fromFileName: stub.fileName)
+    }
+}