This PR adds Google Tag Manager support. Google Tag Manager embedding snippet utility function to push to dataLayer: lib/gtm.js emits custom events like routeChangeStart, routeChangeComplete, and ...
In #62 we implemented the copy function. But in mobile environment, most browsers has a native navigator.share that will trigger share dialog: <https://pjchender.blogspot.com/2019/11/webapis-web-sha>...