Removed reference to nonexisting draggable box in the cube demo
MODULES:LN_GLGUI: Fixed datepicker updating of arrow color.
MODULES:LN_GLGUI: Added timepicker for choosing a time of day HH:MM using arrow buttons.
MODULES:LN_GLGUI: Updated datepicker and timepicker to use specified height.
MODULES:LN_GLGUI: Fixed verticalvaluepicker draw. Create texture once only.
modules: ln_core: make c definitions private to prevent collision
framework: rename CONFIG.h to LNCONFIG.h

this is to prevent collision in coming commits
libz: make cross-compilation work on win32
glcore: add support for reading screen content
png: add module to read and write png images + screenshots
png: fix y orientation and automate power-of-two texture handling

images can now be loaded on the fly with png->img
PNG: Change order of parameters for u8vector->png
Merge remote-tracking branch 'part-cw/master'
defined glMultMatrixf in glcore-ffi.scm and tested on linux and android.