Merge branch 'bc/send-email-auto-cte'

The content-transfer-encoding of the message "git send-email" sends out by default was 8bit, which can cause trouble when there is an overlong line to bust RFC 5322/2822 limit. A new option 'auto' to automatically switch to quoted-printable when there is such a line in the payload has been introduced and is made the default. * bc/send-email-auto-cte: docs: correct RFC specifying email line length send-email: automatically determine transfer-encoding send-email: accept long lines with suitable transfer encoding send-email: add an auto option for transfer encoding