add share/commands/traverse-all-parents
share/commands/diff-list: bug fixed: output unnecessary empty line when one of the input list is empty
share/commands/commit: global id of root change to empty instead of 0000000000000000000000000000000000000000, because i'm not sure whether there would be something whose sha1 value is 0000000000000000000000000000000000000000
share/commands/generate-global-id: all arguments can be optional(empty)
share/commands/init-global-index: don't touch head, leave it absent
share/commands/traverse-all-parents: recursion bug fixed: recursing should precede recording; add Depth-First Traversal comment; bug fixed: parent list array echoed incorrectly
add share/commands/generate-tree-graph