Export FlowRouter so it can be used outside modules

[Jessedev1]

I wanted to use this awesome package in one of my local packages, but it can only be imported into modules.
This can be resolved by simply adding an export of the FlowRouter class.

I've tested it in my project and it works like a charm!

[jankapunkt]

@Jessedev1 apparently you renamed all paths using your local namespace jessedev:ostrio-flow-router-extra you can try to revert this but I'd rather suggest you to use a clean branch, checked out from master (of this repo) and only apply the relevant changes that will not include your local changes.