Until now the prompt only shows the last three levels of the prompt,
however I'd personally prefer to have some more levels (i.e. five).
I figured that it's not worth debating about how many levels make sense,
instead it's now configurable in `~/.zshrc`, the current default will be
kept.
This can be achieved by adding the following line to `~/.zshrc` *before*
loading this theme:
```
export LAMBDA_MOD_N_DIR_LEVELS=5
```
