nucleotides test and example in coffeescript

I squashed the commits together into one and renamed the main file. I think I have done everything correctly, but if there is something else let me know :)
If I am reading this correctly, you probably don't need this (lines 10 - 12). They can be changed to:

```
throw new Error('Invalid Nucleotide') if nucleotide not in @nucleotideCounts
```