replace bigint with node-int64

[lechuhuuha]

This is an attempt to add support for broofa/node-int64.

Summary from this reply:

• Use node-int64 instead of big-integer
• After that performance was increased x20 for large files. (11mb - ~9sec).

If merged, this PR should resolve #38 and #224

[ZJONSSON]

Thanks, @lechuhuuha. Can you clean this PR up (remove the extra newlines) and also remove big-integer from package.json if it's no longer required?

[lechuhuuha]

Yes i will do that
Thanks for point its out

[lechuhuuha]

I had editted the PR
You can check it out @ZJONSSON.

Thanks

[ZJONSSON]

Thanks @lechuhuuha!