Add logs retention
Add threading feature to optimize backup time
Add Default parameter for threading feature
Max child process control -> Limit the number of backup running in parallel
Merge branch 'feature-02' into release-0.3.0
Fix some compression problem
D'ont overwrite mongodb-backup.conf when rerun install.sh
Update some log comments
Add more comments and use lower CamelCase for functions and non-global variable
Fix control child process loop by adding a system delay
Fix Picking secondary funtction
Update Readme and Changelog