Changes

• Reject odd input depths that pixThresholdToBinary doesn't support.
• Fix build with Leptonica >=1.83
• Replace vs2008 solution with CMake
• Fix Error heap-use-after-free
• Fix typos in code
• Support python 3, drop support for python2
• Rename pdf.py to jbig2topdf.py
• Add a switch to set dpi for images w/o dpi information
• Add support for standalone .jb2
• Suppress a chatty informational message unless requested
• Neat symbolic threshold 0.92
• Fix Endian issue on ARM #63
• Neat symbolic threshold 0.92
• Make the weight parameter adjustable
• Add global BW threshold on 8 bpp images
• Replace obsolete macro `AC_PROG_LIBTOOL'