Read TIFF and EXIF information from a JPEG-format image.

1. Retrieve data from a file:

        iex> {:ok, info} = Exexif.exif_from_jpeg_file(path)

   Retrieve data from a binary containing the JPEG (you don't need the whole
   thing—the exif is near the beginning of a JPEG, so 100k or so should
   do fine).
        iex> {:ok, info} = Exexif.exif_from_jpeg_buffer(buffer)

2. Access the high level TIFF data:

        iex> info.x_resolution
        iex> info.model

3. The exif data is in there, too.

        iex> info.exif.color_space
        iex> info.exif |> Dict.keys
        [:brightness_value, :color_space, :component_configuration,
         :compressed_bits_per_pixel, :contrast, :custom_rendered, :datetime_original,
         :datetime_tigitized, :digital_zoom_ratio, :exif_image_height,
         :exif_image_width, :exif_version, :exposure_bias_value, :exposure_mode,
         :exposure_program, :exposure_time, :f_number, :file_source, :flash,
         :flash_pix_persion, :focal_length, :focal_length_in_35mm_film,
         :iso_speed_ratings, :lens_info, :light_source, :max_aperture_value,
         :metering_mode, :recommended_exposure, :saturation, :scene_capture_type,
         :scene_type, :sensitivity_type, :sharpness, :white_balance] 


The exif tag list is missing some of the newer entries. Contributions welcome.

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