fix big TSV file download error

use fs.createReadStream not fs.readFile

If you 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
modify CSV file download logic same as TSV file download
modify head logic using readline
modify show full logic same as TSV file download
use one shib.client() instance
Merge pull request #14 from wyukawa/feature-big-file-read-handling

modify big file read handling