* Installation working as a configuration package
* Fix source listing to not use GLOB per CMake recommendation. Files
  are listed explicitly in `source_files.cmake` so that if file listing
  changes, CMake can detect it and regenerate as needed.
* Added debug postfix for libs for side-by-side installation of different
  build variants (`libzxing.lib` and `libzxing-debug.lib` on Windows)