This flips the AMP instance definitions into canonical form and makes
the code a bit more future proof.

This is needed to silence GHC 7.8's AMP warnings, see also

 http://www.haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal#Missing_superclasses



for more information.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

Minor refactor: represent the prefix as a [Grapheme] in internal functions, rather than as a String.

  Summary of changes:
   - Removed RankNTypes; added Rank2Types, UndecidableInstances
   - Revamped Command interface to be simpler and more monadic
   - Refactored key/command processing into new module RunCommand
   - Begin infrastructure for emacs/vi modes to have their own state.
   - Make Monad boilerplate a little simpler
   - TODO: The Windows build is broken.

Refactor how vi-mode repeated commands are treated.  Also fixes the behavior of dw,cw,ce,etc. (see #86).

Second try:  Ensure that we move past the line after finishing, even if an exception occurs that we didn't control (for example, darcs or ghci's SIGINT handlers).

Refactor; have new type CmdAction; now tab completion paging works properly (overwriting the '--More--' message).

Added optional ctrl-c handling.  If the handleInterrupt setting is True, then on ctrl-c we throw an exception.  Only works with posix, for now.