correct cycle typestack#358, by extracting TransformationType in a se…

…parate file

because:
    * TransformationType enum is used by both TransformOperationExecutor  and MetadataStorage
    * TransformationType was in the same file as TransformOperationExecutor
    * TransformOperationExecutor require MetadataStorage
so: importing TransformationType from TransformOperationExecutor.ts was as a side effect importing MetadataStorage.ts that was importing TransformationType etc. creating a cycle

src/TransformOperationExecutor.ts

@@ -2,12 +2,8 @@ import { ClassTransformOptions } from "./ClassTransformOptions";
 import { defaultMetadataStorage } from "./storage";
 import { TypeHelpOptions, TypeOptions } from "./metadata/ExposeExcludeOptions";
 import { TypeMetadata } from "./metadata/TypeMetadata";
+import { TransformationType } from "./TransformationType";
 
-export enum TransformationType {
-    PLAIN_TO_CLASS,
-    CLASS_TO_PLAIN,
-    CLASS_TO_CLASS
-}
 
 export function testForBuffer(): boolean {
     try {

src/TransformationType.ts

@@ -0,0 +1,5 @@
+export enum TransformationType {
+    PLAIN_TO_CLASS,
+    CLASS_TO_PLAIN,
+    CLASS_TO_CLASS
+}

src/metadata/MetadataStorage.ts

@@ -1,7 +1,7 @@
 import {TypeMetadata} from "./TypeMetadata";
 import {ExposeMetadata} from "./ExposeMetadata";
 import {ExcludeMetadata} from "./ExcludeMetadata";
-import {TransformationType} from "../TransformOperationExecutor";
+import {TransformationType} from "../TransformationType";
 import {TransformMetadata} from "./TransformMetadata";
 
 /**