[Feature Request] Having a copy button to the code blocks highlighted in the showdown. 

Hey there, 
I would appreciate if there were a way so that we also have a copy code button aside to the code we have , I tried to explore other libararies as well for the same . I.e this
https://www.npmjs.com/package/showdown-copy-code?activeTab=readme
But this doesn't seem to work . 
