Add previous member table
Add copy function and refactor codes in member-table
Modify test cases
Implement to copy current-members to prev-members when exec 'rebalance'
Set one or plural target node(s) when executing rebalance-command
Optimize rebalance-related codes
Modify Copyright
Refactor create-fun
Modify create-routing-table#1
Modify create-routing-table#2
Modify create-routing-table#3
Optimize codes of creating ring
Optimize codes of creating ring#2
Modify create-routing-table#4
Modify create-routing-table#5
Modify create-routing-table#6
Modify create-routing-table#7
Merge branch 'feature/manage_prev_and_cur_member' into develop