Added functionality to additonal socialjs containers

[DaneshMadarbakus]

Hi, thanks for creating this plugin in vanilla js, it is very useful!

While using it for one of my projects I noticed that I wasn't able to place multiple socialjs containers on the page to create multiple twitter share buttons sharing different URLs so I've added the ability to do this and updated the documentation.

Changes made to src folder file, had some issues with grunt settings and couldn't minify and compile.