Use shFlags to parse flags given to main and subcommands.

Implement the flags for each of the 'feature' subcommands.
diff --git a/git-flow b/git-flow
index 4179fde..303e8a7 100755
--- a/git-flow
+++ b/git-flow
@@ -80,12 +80,13 @@
 	# run command
 	. "$GITFLOW_DIR/git-flow-$SUBCOMMAND"
 
-	#
-	# TODO: How to handle 'git flow feature --verbose'
-	#          instead of 'git flow feature list --verbose'
-	#       "--verbose" is not a subcommand!
-	#
-	SUBACTION="${1:-default}"; shift
+	# test if the first argument is a flag (i.e. starts with '-')
+	# in that case, we interpret this arg as a flag for the default
+	# command
+	SUBACTION="default"
+	if [ "$1" != "" ] && ! echo "$1" | grep -q "^-"; then
+		SUBACTION="$1"; shift
+	fi
 	if ! typeset -f cmd_$SUBACTION 2>&1 >/dev/null; then
 		warn "Unknown subcommand: '$1'"
 		usage