Merge pull request #23 from ahusseini/issue/22

dictionary returned from sign function now includes headers passed to it

Sources/AWSSignatureV4/AWSSignatureV4.swift

@@ -192,11 +192,19 @@ extension AWSSignatureV4 {
             signature: signature,
             signedHeaders: signedHeaders
         )
-
-        return [
+
+
+        var requestHeaders: [HeaderKey: String] = [
             "X-Amz-Date": amzDate,
             "x-amz-content-sha256": payloadHash,
             "Authorization": authorizationHeader
         ]
+
+        headers.forEach { key, value in
+            let headerKey = HeaderKey(stringLiteral: key)
+            requestHeaders[headerKey] = value
+        }
+
+        return requestHeaders
     }
 }