Enhance `haskell-version` to show more information

This commit marks `haskell-version` autoloaded and `M-x
haskell-version` now echos more information, e.g.

 "haskell-mode version 2.9.1 (2.9.1-93-gb76e104-dirty @ /home/hvr/.emacs.d/elisp/haskell-mode/)"

This style has been copied from Org mode's `org-version`.
Add new `make package` target for creating ELPA packages

This new target generates a package distribution file

  haskell-mode-<release-version>.tar

(where <release-version> is inferred by `git describe --tags --abbrev=0`)
according to the guidelines described in

  http://www.gnu.org/software/emacs/manual/html_node/elisp/Packaging.html

which can then be installed directly via
`M-x package-install-file` (or uploaded to Marmalade)

This addresses #156 and #92