Add the ability to change page by pressing the button?

[KINGAWESOME266]

I am interested in using PywebIO for multiple projects, and I have created a simple test application. However, a crucial feature that I would need from PywebIO is the ability to use the put_button as a relative link. If I were to use pywebio with Flask, and set the routes just like in the documentation here, I would like to have the ability to define a relative link like /help, /about etc.

An example way to implement this is to have an extra attribute to set when using put_button like link='/help', just like in HTML and Markdown, you can use relative links such as '/help'.

[wang0618]

You can use pywebio.output.put_link(), #352 is also helpful