Add annotations with `timew track`

I record my time using the `timew track` command, and I use annotations for recording descriptions.

Currently, I run a command similar to this:

```
timew track interval tags && timew annotate @1 annotation
```

This can be error prone. If I am backdating an interval, I need to look up its id, in order to add an annotation to it.

It would be nice to have a command line switch, maybe `-a` or `--annotate`, so that I could write the command above as:

```
timew track -a annotation interval tags
```