Adds a `border!` macro that takes TOP, BOTTOM, LEFT, RIGHT, and ALL and
returns a Borders object. An empty `border!()` call returns
Borders::NONE
This is gated behind a `macros` feature flag to ensure short build
times. To enable, add the following to your `Cargo.toml`:
```toml
ratatui = { version = 0.21.0, features = ["macros"] }
```
Co-authored-by: C-Jameson <booksncode@gmail.com>
