Merge branch 'bg/send-email-smtpdomain' into maint

* bg/send-email-smtpdomain:
  send-email: Cleanup smtp-domain and add config
  Document send-email --smtp-domain
  send-email: Don't use FQDNs without a '.'
  send-email: Cleanup { style

diff --cc Documentation/config.txt
Simple merge

diff --cc Documentation/git-send-email.txt
Simple merge

diff --cc git-send-email.perl
Simple merge