implemented TGLui_RoundRectangle & TGLui_FilledRoundRectangle

- implemented TGLui_RoundRectangle & TGLui_FilledRoundRectangle
 in glui_primitives.pas
- updated the DevDemo1 with 3 instances of each class.
- changed the way the constant Glui_CircleSampling is interpreted
Merge https://github.com/B4Z1l3/Glui