bindings() and setBindings() are not present in the browser version of pino

Hello!

I was attempting to use pino in the browser today and discovered that .bindings() is undefined. Additionally, .setBindings() is also undefined, but it's also undocumented in general (is it officially part of the API?).

I looked into adding this to browser.js but I'd definitely need some guidance before proceeding. For example, I'm not sure if bindings changes cascade through child loggers or if they are fixed at the time of child creation, for example.