Adding System.fetch/2

[spencerdcarlson]

Fetch env by varname and return a default if the varname is not set. Handle String.to_integer inferred from default type

[josevalim]

The default value should be added to System.get_env/3, as to mirror the Map/Keyword API -- *José Valim* www.plataformatec.com.br Skype: jv.ptec Founder and Director of R&D

[josevalim]

Sorry, System.get_env/2. You should be able to add a default argument to the existing implementation. Then you just need to update the docs and add tests. :) -- *José Valim* www.plataformatec.com.br Skype: jv.ptec Founder and Director of R&D

[guilleiguaran]

@josevalim I sent a PR for get_env some time ago: #3798 and was rejected, I can rebase it if you changed your mind about the reasons 😅

[josevalim]

Perfect, I will merge it then. Thank you @spencerdcarlson and @guilleiguaran !