image: fix ARGB png randering

Initial patch provided by limxuzheng.

Github-hook: fix #43
topwin: use postorder traversal in _rtgui_topwin_draw_tree
topwin: show from the activated window in rtgui_topwin_activate_topwin

When topwin A is going to be activate, _draw_tree from A instead of the
root of the topwin. As the parents of A should have already been shown.

Thanks for limxuzheng and hexlog for bug reporting.

Github-hook: fix #39
textbox: get the font_width on the fly

If the user changed the font on the fly, this commit makes caret right.

Thanks to hexlog for providing the patch.

Github-hook: fix #35
textbox: fix a regression in caret setting
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.
edit: support wide char key event
widget/textbox: fix the wide char support
widget/textbox: treat the text as unsigned char
simulator: init the SDL after DFS

SDL init would need DFS, which is in rt_components_init.
simulator: include Windows.h only when _WIN32 is defined
Add rockbox fnt font; remove compiling warning
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.