format-patch is invoked, but in addition can be set to "auto", to
generate a cover-letter only when there's more than one patch.
+format.outputDirectory::
+ Set a custom directory to store the resulting files instead of the
+ current working directory.
+
filter.<driver>.clean::
The command which is used to convert the content of a worktree
file to a blob upon checkin. See linkgit:gitattributes[5] for