Add option to merge extracted strings with existing translations (Thanks to @ocombe)

src/compilers/compiler.interface.ts

@@ -0,0 +1,9 @@
+import { TranslationCollection } from '../utils/translation.collection';
+
+export interface CompilerInterface {
+
+	compile(collection: TranslationCollection): string;
+
+	parse(contents: string): TranslationCollection;
+
+}