3.0.0 Release

[nblumhardt]

This is a major update to the sink, switching to MailKit on all platforms, and with new configuration methods including JSON configuration syntax.

• 87 - support MailKit's SecureSocketOptions (@arthurchiakh)

• 98 - extract email transport from sink (@mgrosperrin)

• 97 - support batched email with headers and footers (@0xced)

• 122, #123 - use MailKit on all platforms, redesign configuration methods, drop obsolete TFMs (@nblumhardt)

Breaking changes

• Drops support for netstandard1.x and net45
• Now relies on MailKit for email delivery on all target platforms
• Redesigned WriteTo.Email() configuration method and parameters mean code and JSON configuration will need to be updated, see README.md for details

[nblumhardt]

There's probably no easy way to release this one except to "rip the Band-Aid off" and merge it. The new README is much more detailed and useful than the old one, so queries should be fairly easy to route.

I'll leave this open for a few days to give everyone a chance to chime in :-)

[MidgeOnGithub]

It seems this may have been forgotten; bumping for your visibility! (:

[nblumhardt]

Thanks @MidgeOnGithub :+1: