Introduce @since module attribute

[josevalim]

It can be stored alongside the documentation. My suggestion is to support @since for now, so we at least have the information in the source code but to store them with the docs would require to redesign the docs chunk, something we are trying to do with the consensus of all other BEAM languages.

[albertoalmagro]

Could I try this one @josevalim ? Could you please give me an example of a similar already existing feature?
Thanks!

[whatyouhide]

@albertoalmagro you can look at how we store @doc for starters. However @josevalim assigned himself so maybe he wants to tackle this one.

[josevalim]

I assigned this one to me because I am already working on it. :)

[albertoalmagro]

Thanks @josevalim @whatyouhide this one looked interesting 😉

[eksperimental]

I guess this one can be closed