Replace doxygen-style docs

Avoid doxygen-style docs (`@param`, etc.), `cargo doc` does not understand this format, at least natively.

This is more idiomatic if arguments/returns need descriptions:
```rust
/// Description...
///
/// # Arguments
///
/// - `a`: $\alpha$ - ...
/// - `b`: $\beta$ - ...
///
/// # Returns
///
/// Something nice.
```