Add a CLI for Bronto.

Uses [Mercenary](https://github.com/jekyll/mercenary) to implement a very simple CLI:

```bash
~/code/bronto$ ./bin/bronto unclear fish tank
Fetching synonyms for 'unclear'...
  No results.

Fetching synonyms for 'fish'...
  verb: angle, catch, grab, look for, search, seek, take hold of
  noun: aquatic vertebrate, food, individual, mortal, person, pisces, pisces the fishes, solid food, somebody, someone, soul

Fetching synonyms for 'tank'...
  No results.
```

No clue if you even want this, but figured it would be an easy standalone implementation example for the library.