* Put information about the compiler pass in the _source field of Diagnostic
It's useful when looking at the hie-core command-line output to see where
a problem is coming from.
* include test code in hie-core's own cradle
* Add a .gitignore just for the hie-core piece
* Add standalone pieces to make hie-core work with a global Cabal install
* Add more things to .gitignore, PR suggestion
* Add copyright header
