Remove `dist` target hack

This removes quite a bit of Makefile hackery and finally resolves #156.
Add ELPA-compatible README

This is needed for `marmalade-repo.org` as it doesn't read the comment
section of `haskell-mode.el`.
Add texinfo manual skeleton

This is mostly to set up the infrastructure needed for distributing an
Info manual. This commit also adds a few references from docstrings to
Info nodes for testing.

When installing via MELPA/Marmalade, the info file location should be
automatically registered, however when working directly from git
checkout the following is needed:

    (add-to-list 'Info-default-directory-list "~/<some-folder...>/haskell-mode/")