Create Grails 3.x compatible version

[mansi90]

No description provided.

[jakubnabrdalik]

What's left:

• upgrade test app (https://github.com/TouK/excel-export-samples) to current version
• update readme
• publish

[jakubnabrdalik]

And perhaps change API to have functional interfaces only, so that you can use closures.

[mansi90]

I already created one on Grails-3.0.2 for this plugin, following is the github url:
https://github.com/mansi90/demo-excel-export-grails3

But, I'll update @jakubnabrdalik's sample application (https://github.com/TouK/excel-export-samples) as well. Today, I am little busy, so will start work on this by tomorrow. Please let me know of any other issues or concerns.

[jakubnabrdalik]

Actually this was kind of a note to myself, :) because I won't be able to give it a shot before Sunday. But if you can do it it would be awesome.

Thank you.