Change Handler's MonadState instance to use state of v rather than Sn…
Removed unused language extensions.
Refactor so the Heist snaplet doesn't import stuff from Internal.
Rename Snap.Types to Snap.Core
Switched from fclabels to data-lens.
Changed type variable e to v everywhere.
Add deleteFromSession to Snaplet.Session
Renamed withChild and withSibling, and removed withBase.
Alpha release of new snaplet infrastructure.