Hint with buffer names when using C-k with emacs

Fixes #606
joinLinesE: cosmetic
Fix up cabal file a bit
cd and pwd functions

Fixes #587

My initial attempt was to use file hints and filter out anything that's
not a directory but that turned out a bit tricky: we can't do it just by
converting default file hints as we're missing directory information. We
just need to pass what's being typed into the box as an extra value to
the hinter
Hinting for M-x cd
Fix optparse-applicative constraint

https://github.com/feuerbach/tasty/issues/81
disambiguate import in presence of regex-tdfa-rc
Implement C-x C-r (#581)
Fix display of paths starting with /

Fixes #528
Write binary instances by hand in Yi.Types

This stops the stupid TH scoping problems seen in 7.8.3
Don't mark buffer as changed if nothing was killed

Fixes #618
Remove Ref typeclass

MVar and IORef have different semantics (MVar can be empty, IORef
can't), so this typeclass isn't all that useful. In addition, it's not
used all that much, and only to automatically liftBase!