Remove unused image processing parameters

This change removes the autoconvert and format parameters. In all call
situations they were either not set or set to the default value anyway.
Pass settings dictionary to generate_image

Reduce the amount of parameters to pass necessary to generate an image.
Add adjust_options

This gives the user the ability to process the images after resizing them. In
particular, the color, contrast, brightness and sharpness can be adjusted.
Update CONTRIBUTING
Merge pull request #30 from matze/adjust-images-after-resizing

Adjust images after resizing
Read GPS coordinates from EXIF tags

If GPS information can be found in the EXIF tags, latitude and longitude will be
extracted and added to the `media.exif.gps` variable. Some ideas how to get the
GPS tags from the EXIF tags where borrowed from Eran Sandler's gist (licensed
under MIT license):

    https://gist.github.com/erans/983821
Add test case for GPS tags

This also adds a sample image licensed under CC-BY-NC from jerquiaga located at
Flickr: http://www.flickr.com/photos/jerquiaga/2394751088/
Merge pull request #29 from matze/exif-gps

Read GPS coordinates from EXIF tags
More tests for get_thumb
Pilkit 1.1.2 needs a file pointer for save_image
Remove obsolete --use-mirrors option
Add flask theme
Change to flask theme and customize.
Split documentation in multiple pages.
Docs for bundled themes, pillow ...
Update changelog
Add the changelog to pypi description.
Fix bug because of an extra param in video.generate_thumbnail
Remove null bytes at the end of the DateTimeOriginal exif tag.
Use exif metadata in the themes.