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
Adapt Makefile to consider only tags matching `v[0-9]*` (re #145)
Add tarballs to "clean"-target
Tweak VERSION to avoid leading 0s

The release version has to be in normal form (i.e. `13.6` instead of
`13.06`) as otherwise ELPA-like repositories such as Marmalade
misbehave.
Convert coding of `haskell-{doc,mode}.el` to UTF8

These two are the only elisp files left still using iso-8859-1 for
non-ASCII characters, and might have been the cause for issues such
as #157
Fix Makefile to leave less temporary files behind
Add `haskell-unicode-input-method.el` to distribution (re #13)

This also integrates

 https://github.com/roelvandijk/emacs-haskell-unicode-input-method/blob/master/README.markdown

into haskell-mode's README.md
refactored & improved README