Using setuptools and changed way versioning is done

Hi Ianare,

i saw that you have already included some of the modification i did on my fork of your exif-py. I merged those back to my fork and did a few more modification, which i put in this pull request. I hope i did it right, since i'm still more accustomed to svn than to git. I did not change too much:

* i switched from distutils to setuptool and made the EXIF.py script an entry point insteat of a script
* the version number is now in exifread.__init__ and is imported in both the setup.py and the EXIF.py to use with the -v switch

I have a few more things in mind so you can expect some more pull requests if this one works as expected.

Regards,
Peter