Missing player input keys
In the manual for 0.1.2, it says:

```
Player 1 keys: Cursors + ZX / NM
Player 2 keys: SDFE + tab,Q / shift A
```

from the keymap defined in main.lua:

```
__keymap = {
    [0] = {
        [0] = 'left',
        [1] = 'right',
        [2] = 'up',
        [3] = 'down',
        [4] = 'z',
        [5] = 'x',
    },
    [1] = {
        [0] = 's',
        [1] = 'f',
        [2] = 'e',
        [3] = 'd',
        [4] = 'q',
        [5] = 'a',
    }
}
```

it looks like the `nm`/`lshift/a` is missing.

This would be nice to add for familiarity with the picolove system!
