image: fix ARGB png randering

Initial patch provided by limxuzheng.

Github-hook: fix #43
topwin: fix a regression in fcda3a5f887

When we have multiple window tree and the parent is clipped by others,
activate child window don't get the parent to be repainted. Define
RTGUI_ONLY_ONE_WINDOW_TREE if your application only have one window tree
so we could do some optimization.

Conflicts:

	components/rtgui/server/topwin.c
topwin: use postorder traversal in _rtgui_topwin_draw_tree
RTGUI: implement object id
demo_view_window: utilize the object id
add gcc.ld
add GPLv2 LICENSE
RTGUI: add RTGUI_USING_ID_CHECK option

When this option enabled, it will make sure the id setted in
rtgui_object_set_id is unique per application. However, this could take
a long time when there are many widgets. So when you are sure about your
id, it's better to turn this off.
RTGUI v0.7
RTGUI: fix a compile error on MDK and GCC
realtouch: remove unused code
fix linking error on Linux
widgets/textbox: port compiling warning fix from Bernard
RTGUI: fix some compiling warning in MDK

MDK will complain about "warning:  #1-D: last line of file ends without
a newline" if the source file is not ended with a newline.