Add license

[sregg]

Hi there.

First of all, thank you for this awesome library.
I use it in my company and it works perfectly.
The only issue we have is that it's missing a license.
Would you be able to add one?
Thanks a lot!

[mitoyarzun]

Already responded by e-mail, but if other people are interested I'll put it here too:

I'm working on a huge code update, mostly to address the issues #15 #17 #9 .

When that is ready (hopefully this week) I'll add the license for this project. As far as I understand I should use Apache 2.0 because the original library (https://github.com/zxing/zxing) uses it.

If anyone has any comments on this I'll appreciate the feedback :)