Fixing these warnings required changes to the file names of the `MessageHeader`
struct which makes this commit an API change. The version in the cabal file
has been bumped accordingly.

- Return of the newlines: Add all newlines once again
- Provide better comments
- Remove `sender`
- Consistently use set and get prefixed functions

This allows removing the unix dependency for ipython-kernel, and seems
like the right thing to do as the Stdin module is very specific to the
case of running a Haskell kernel.

Separating packages not working so well.