#189, fix Options type definition and allow custom resolvers.

Author: RopoMen

lib/index.d.ts

@@ -240,6 +240,8 @@ declare namespace SwaggerParser {
       external?: boolean;
       file?: Partial<ResolverOptions> | boolean;
       http?: HTTPResolverOptions | boolean;
+    } & {
+      [key: string]: Partial<ResolverOptions> | HTTPResolverOptions | boolean | undefined;
     };
 
     /**