support single letter parameters

Some commands only have short parameters. This makes them much better.

For the following input:

```
AwesomeSpawn.run("cm", f: "file1", k: "file2")
```

before pr:

```
cm --f file1 --k file2
```

after pr:

```
cm -f file1 -k file2
```

While `"-f" => "file1"` is a viable option, once you do that, you might as just use `["-f", "file1"]` or even `run("cm -f file1 -k file2")`.

Since I don't think there exist single letter long options (e.g.: `--f`), I don't think this change will adversely affect users, but it should be in the changelog.