Add `onAllFiles` which accepts a callback of type `Array<File>->Array<File>` so you can work on all the files at once.
For `onExtension` `*` now means run the callback on all files. Possibly pointless because of `onAllFiles` but they run at different times.
Merge pull request #8 from skial/any_and_all_files

Add `onAllFiles` which accepts a callback of type `Array<File>->Array<Fi...