Add `epe-theme-dakrone`.

epe-theme-dakrone is similar to the epe-theme-lambda, however instead of
reducing the pwd to a single directory, it shrinks it if it's larger
than 3 directories.

Examples:

```
cd ~/src/elasticsearch/src/main/java/org/elasticsearch
~/s/e/s/m/java/org/elasticsearch:feature/input-validation* λ| 

cd /usr/local/Cellar/emacs/HEAD/
/u/l/Cellar/emacs/HEAD:master λ|
```