add extract thumbnail image from exif data functionality and some code fixes and improvements. details:
1. use strict added to prevent global space pollution
2. added comments to some code parts
3. slicing only first 128KB of the original image file - this way the initial ViewData buffer being created much faster! exif data should be always less then 64kbX2
4. log masseges are now handled by local function
5. refactoring variable names within some functions
6. exif thumbnail image IFD tags added
7. the thumbnail data (if found) will be extracted into exifdata.thumbnail property