Remove set_gc/get_gc/get_rect etc interface for DC class.
Merge pull request #61 from nongxiaoming/master

add the filedialog
Merge branch 'master' of https://github.com/RT-Thread/RTGUI
Implement pixel_format feature in buffered DC.
Update .gitignore file.
Support block image transfer a buffered DC to a buffered DC.
If the rect of mainwin is not set when set a graphic driver, the rect of mainwin is set to the rect of graphic driver.
Add _UI_MIN/_UI_MAX/_UI_BITBYTES macro and change the version to 0.8.1.
Dispatch the command event to each tab page of notebook.
Fix the draw point issue in dc_buffer.
Fix the ncolors of palette not initialized issue.
widget: edit/textbox: use text_encoding to deal with encoding

text_encoding provide APIs to deal with variable length encoding. Port
edit and textbox to it.
widget: text_encoding/textbox: fix compiler warnings