(Bash) Do not use `readlink` command for compatible with Mac OSX
(Bash) Auto install sub modules at first
(Bash) Source tmux-completion.bash

1. Sub module add tmux: _bash/sub_modules/tmux
2. Source the tmux-completion.bash
(Bash) Source the homebrew-completion.bash

1. Sub module add homebrew: _bash/sub_modules/homebrew
2. Source the homebrew-completion.bash
(Bash) Source tig-completion.bash

1. Sub modules add 'jonas/tig'
2. Source tig-completion.bash direct from 'tig' sub module.
(Bash) Source git-completion.bash direct from 'git' sub module

1. Sub modules Add 'git' repository: _bash/sub_modules/git
2. Source git-completion.bash direct from the git repository.
(Bash) Source git-prompt.sh direct from 'git' sub module
(Bash) Enhancement \`cd\` command

1. Update the aliases about `cd` command
2. Add cd() function for enhance `cd` command
(Bash) Add git_branch() function to Display the git branch
(Bash) Add git_since_last_commit() to get the time since the git last commit
(Bash) Update bash-completion.sh
(Bash) Update shell-prompt.sh