Merge branch 'sh/am-keep-cr'

* sh/am-keep-cr: git-am: Add tests for `--keep-cr`, `--no-keep-cr` and `am.keepcr` git-am: Add am.keepcr and --no-keep-cr to override it git-am: Add command line parameter `--keep-cr` passing it to git-mailsplit documentation: 'git-mailsplit --keep-cr' is not hidden anymore