add bash completion support

This fixes #188.

bash-completion/rc-status

@@ -0,0 +1,31 @@
+# Copyright (c) 2017 The OpenRC Authors.
+# See the Authors file at the top-level directory of this distribution and
+# https://github.com/OpenRC/openrc/blob/master/AUTHORS
+#
+# This file is part of OpenRC. It is subject to the license terms in
+# the LICENSE file found in the top-level directory of this
+# distribution and at https://github.com/OpenRC/openrc/blob/master/LICENSE
+# This file may not be copied, modified, propagated, or distributed
+# except according to the terms contained in the LICENSE file.
+
+#
+# rc-status completion command
+#
+_rcstatus()
+{
+	local cur
+	cur="${COMP_WORDS[COMP_CWORD]}"
+	if [[ $COMP_CWORD -eq 1 ]]; then
+		if [[ "${cur}" == --* ]]; then
+			COMPREPLY=($(compgen -W '--all --list --unused' -- ${cur}))
+		elif [[ "${cur}" == -* ]]; then
+			COMPREPLY=($(compgen -W '-a -l -u' -- ${cur}))
+		else
+			COMPREPLY=($(compgen -W "$(rc-status --list)" -- ${cur}))
+		fi
+	else
+		unset COMPREPLY
+	fi
+	return 0
+} &&
+complete -F _rcstatus rc-status