Feature request: lint tree files for indenting

[PaulRBerg]

This is more like a nitpick, but properly formatted *.tree file should have:

• Three spaces before beginning of new line and ├──
• Three spaces before beginning of new line and └──
• Two spaces in between │ and ├──
• Two spaces in between │ and └──
• Two spaces in between │ and │

Here's an example of a properly formatted tree:

RefundableAmountOf_Integration_Concrete_Test
├── given null
│  └── it should revert
└── given not null
   ├── given balance zero
   │  └── it should return zero
   └── given balance not zero
      ├── given paused
      │  └── it should return correct refundable amount
      └── given not paused
         ├── when total debt exceeds balance
         │  └── it should return zero
         └── when total debt does not exceed balance
            └── it should return correct refundable amount