Image resize process now deletes temp file after use

ImageManager::resize and ImageMagickResizeAdapter were producing
temporary files during the resize process that were not removed, thus
polluting the /tmp directory. Such files are now deleted after the
process terminates.
Formatted the comment
Merge pull request #120 from elcodi/feature-remove-resized-image-temp-files

Image resize process now deletes temp file after use