Proposal: move github.com/gobuffalo/x/mail into Buffalo "Core"

[markbates]

The github.com/gobuffalo/x/mail seems to be pretty stable, based off of my usage. I think it would make a great addition to core.

The argument for it would be that lots of people send emails from applications, so it should be baked in.

I don't see any cons to bringing it in.

The plan for migration would be to copy the package to github.com/gobuffalo/buffalo/mail, but leave the old x/mail package where it is, but updated the README.md to point out that package is no longer being maintained in favor of the one in the buffalo repo. This is similar to what happened what Go moved context.Context in 1.7.

I'm looking for opinions, pros and cons on this, so please speak up. :)

[stanislas-m]

+1. Sending emails is a common use-case, it makes sense to add it to the core.

[seblw]

Optionally you could just move x/mail content to buffalo/mail, and create a type alias from x/mail to mail (new feature in Go 1.9, https://github.com/golang/proposal/blob/master/design/18130-type-alias.md), but that would require locking buffalo on Go 1.9.

[markbates]

Type aliases, for now are out. Buffalo has a minimum supported version of 1.8.1 so we can’t break those users yet. When 1.10 comes out the minimum version will go to 1.9 and then we can use aliases.

[stanislas-m]

@markbates, just my 2 cents: since the default Buffalo setup includes i18n configuration, does it make sense to add a similar config for the mailer generator? (since we can't use the one from the actions package, because of circular deps)