Option Completion

• Optional Completions: some command completions that like -*, such as --global in git config --global.
• You should use option completion first.
• Taking git as an example, if you want to enter git config user.name --global xxx, you should use --global completion first, and then use user.name, and then enter the name xxx.
• For options ending with =, if there's completion definition, you can directly press the Tab key to get the completions.