Adds Ability to customize Folio Routes

[inmanturbo]

This extracts the Rout:: calls in Folio::route() to an invokable class, and adds a loader parameter to Folio::route() where a custom loader can be passed as a callback function or Closure.

• By default the behavior doesn't change so it shouldn't break anything
• The package will still pass $this->handler($mountPath) but its use is optional
• Users are free to call their own custom handler which can be used to extend functionality such as supporting different file extensions, etc.
• Users are free implement their own names and naming patterns for routes

[taylorotwell]

I may consider this in the future.