Specification change for the free trial period

@August 2, 2021

Users can serve the one-week free trial when first creating the　account.

During the free trial, users can use all the features available in the Premium plan except that the input texts are saved on our server.

With the above change, users will be able to use the free trial without registering a credit card.

Change the color of the output of the rewrite function

@August 2, 2021

Changed the highlight color (insert, delete) in the output of the rewrite function.