Package type choices not Colorblind friendly
Nimble Package type choices are not Colorblind friendly.

![nimble-colors](https://user-images.githubusercontent.com/1189414/48308844-523f7b00-e54b-11e8-8afc-e02c4e20c5b9.jpg)

I am not colorblind and can barely distinguish the options, sure a colorblind user will have a hard time.

Should be an easy Fix, keep colors, add arrows, like:

```
Choices: library <--
         binary
         hybrid
```

[On fonts with ligatures it should display like an actual pretty arrow](https://github.com/tonsky/FiraCode#fira-code-monospaced-font-with-programming-ligatures).

Lets make Nimble more accesible for everyone.
:smile_cat: 