\## Motivation

Monkeytype has the possibility of training just the words that you miss
and this seems like a straight forward thing to add.

\## Implementation

Main change is to add a mssed_words item to the Result struct

```rust
pub struct Results {
    pub timing: TimingData,
    pub accuracy: AccuracyData,
    pub missed_words: Vec<String>,
}
```

And on the Results State, listen for 'p' (practice) to start a new test
from missed words.

```rust
state = State::Test(Test::from_missed_words(&result.missed_words));
```

For the `Results` struct I did a very small refactor in the
`From<&Test>` Trait implementation. I moved the calculation of each
result to its own function, to leave the From function easier to follow.

```rust
Self {
    timing: Self::calc_timing(&events),
    accuracy: Self::calc_accuracy(&events),
    missed_words: Self::calc_missed_words(&test),
}
```