Merge branch 'sd/format-patch-to'

* sd/format-patch-to:
send-email: add --no-cc, --no-to, and --no-bcc
format-patch: add --no-cc, --no-to, and --no-add-headers
format-patch: use a string_list for headers
Add 'git format-patch --to=' option and 'format.to' configuration variable.