Add LodePNG library.

.gitignore

@@ -12,8 +12,10 @@
 build
 *~
 *.o
+*.obj
 *.bak
 *.dep
 *.lib
 *.a
-
+*.i
+*.d

components/external/lodepng/SConscript

+from building import *
+
+cwd = GetCurrentDir()
+src = Split('''
+lodepng.c
+''')
+
+CPPPATH = [cwd]
+
+group = DefineGroup('lodepng', src, depend = ['RTGUI_IMAGE_LODEPNG'], CPPPATH = CPPPATH)
+
+Return('group')