Added script to convert Social Security data dumps to JSON

This tackles the "Better names" point from the todo list.

How to use:
1. Go to http://www.ssa.gov/oact/babynames/limits.html, download and unzip the dumps.
2. Convert to JSON with the following syntax: `node yob-to-json.js <filename> [threshold]`

Example output:
```shell
$ node yob-to-json.js yob2013.txt 10000
{"firstNames":{"male":["Noah","Liam","Jacob","Mason","William","Ethan","Michael","Alexander","Jayden","Daniel","Elijah","Aiden","James","Benjamin","Matthew","Jackson","Logan","David","Anthony","Joseph","Joshua","Andrew","Lucas","Gabriel","Samuel","Christopher","John","Dylan","Isaac"],"female":["Sophia","Emma","Olivia","Isabella","Ava","Mia","Emily","Abigail","Madison"]}}
```

`threshold` is the number of times the name must be used, so that it is included in the output.
The generated JSON data can directly be pasted into ChanceJS source.