Support install of package options

[yunti]

Currently when trying to add packages to be installed with pipenv to the pipfile such as

django-storages[boto3]
django-anymail[mailgun]

these generate a syntax error with the TOML format.

It's not clear from the docs (or past issues) whether these are supported or what the alternative should be?

[yunti]

Found in the pipfile docs
eg
requests = { extras = ['socks'] }