added json dict format

I use it all the time... (see [demo](http://converter.vis4.net/))

**Sample input 1:**

```csv
State	Obama
Alabama	38.36
Alaska	40.81
Arizona	44.45
Arkansas	36.88
```

Output:

```json
{
  "Alabama": 38.36,
  "Alaska": 40.81,
  "Arizona": 44.45,
  "Arkansas": 36.88
}
```

**Sample input 2:**

```csv
State	Obama	Romney	Other
Alabama	38.36	60.55	1.10
Alaska	40.81	54.80	4.39
Arizona	44.45	53.48	2.07
Arkansas	36.88	60.57	2.55
```

Output:

```json
{
  "Alabama": { "Obama":38.36, "Romney":60.55, "Other":1.10},
  "Alaska": { "Obama":40.81, "Romney":54.80, "Other":4.39},
  "Arizona": { "Obama":44.45, "Romney":53.48, "Other":2.07},
  "Arkansas": { "Obama":36.88, "Romney":60.57, "Other":2.55}
}
```