Refine `GinEdit`, `GinDiff` or else.

[lambdalisue]

• I don't remember the command syntax so I'd like to open a corresponding buffer without command arguments
  • GinEdit to open index content of the current buffer
  • GinEdit HEAD to open HEAD content of the current buffer
  • GinDiff to open index diff of the current buffer
  • GinDiff HEAD to open HEAD diff of the current buffer
• I'd like to open working tree file with single command