Enable to mask texts (#73)

* chore: reorder options

* feat: enable to mask texts

* feat: add the default mask function

* refactor: rename options to identify the difference between  mask text and mask input

* test: add tests about masking

typings/types.d.ts

@@ -86,3 +86,4 @@ export declare type SlimDOMOptions = Partial<{
     headMetaAuthorship: boolean;
     headMetaVerification: boolean;
 }>;
+export declare type MaskTextFn = (text: string) => string;