using `-m` or `--merges-only` will only show the merge
commit messages. It will also use the body of the merge
commit message in addition to the subject, as github merges
usually have a useless subject line for commit messages.
If used with `-n/--no-merges`, the last one specified will win.
Although Github reserves the 'visionmedia' user space(a visit to there
will be redirected to 'tj'), it's better to
rename the links from visionmedia/git-extras to tj/git-extras