Scale2x Scale3x GUI

PNG rescaling Scale2x and Scale3x utilities, including batch rescaling programs.

Added some progress indicators to GUI, useful when upscaling big files, especially in batch mode.Some readability improvements on code, especially includes.For Windows users, compiled Windows 64-bit exe builds are added. Windows 64-bit exe are distributed using solid self-extracting 7zip archive; programs are quite self-contained and do not change a thing in your system, so simply start the self-extractor and extract them anywhere you want, you can easily move or delete them as you wish later.