modify big file read handling

If I download big TSV file(for example, 4GB), the following error occurs.

```
buffer.js:194
this.parent = new SlowBuffer(this.length);
^
TypeError: Bad argument
at new Buffer (buffer.js:194:21)
at fs.js:220:16
at Object.oncomplete (fs.js:107:15)
```

I refer https://groups.google.com/forum/#!topic/nodejs_jp/M3cVWLo7ZFU

So, I modify code by using fs.createReadStream not fs.readFile.

I think that there are 4 places to use fs.readFile.

* show full
* show head
* tsv
* csv

So, I modify 4 place.