outrun/outrun-core/lib/subtraction.outrun

use Any
use Option

```doc
# Subtraction

Values which wish to implement the `-` infix operator must implement this protocol.
```
protocol Subtraction, as: do
  ```doc
  Subtract `other` from `self`, returning an option.

  It is left up to the implementer to define when it should return `Some` or `None`.
  ```
  def subtract(self: Self, other: Any): Option
end