Added HTTP Stream API and indicator of clipped MCUs to draw callback

This release adds the open() method to work with streams and provides a new variable to the JPEGDRAW callback (iWidthUsed). For images which are not an exact multiple of MCUs wide, this variable allows you to know when to clip columns off the right edge, but doesn't change the bytes-per-line behavior of the output pixels. For example, if a non-subsampled color image is 33 pixels wide, the JPEGDraw callback will provide strips of pixels 40 wide (5 x mcu width 8). For the call containing the right edge, the iWidthUsed variable will be different from the iWidth variable to alert you of pixels to be clipped.