Add thick_line routine; fix ARGB888 blit issue when the pixel format of source and destination is same.
Add _UI_ABS macro to get absolute value.
Remove the temporary buffer to reduce memory usage.
Merge pull request #64 from BernardXiong/master

Remove the temporary buffer to reduce memory usage.
Merge branch 'master' of https://github.com/BernardXiong/RTGUI
Merge branch 'master' of https://github.com/RT-Thread/RTGUI
Add gesture feature.
Add SDL2_gfx copyright
Merge pull request #65 from BernardXiong/master

Add gesture feature.