## Make the Deadfish swim

Write a simple parser that will parse and run Deadfish.

Deadfish has 4 commands, each 1 character long:

- `i` increments the value (initially 0)
- `d` decrements the value
- `s` squares the value
- `o` outputs the value into the return array

Invalid characters should be ignored.

```rust
parse("iiisdoso") => [ 8, 64 ]
```