Ability to prevent leaking of globals from the concatenation

[vitalybe]

Feature suggestion:

Currently the files are simply concatenated. It would be nice to have an option to concat multiple files, but then lock them all in some kind of scope.

Even better, if it could work together then with something like expose-loader.

[hxlniada]

sounds good, i will try, maybe next week.
feel free to send a pr.
thank you.